Acryl-base polymer film, optical compensation film, and liquid-crystal display device having the same

ABSTRACT

The invention relates to an optical compensation film for IPS or FFS-mode liquid crystal display devices, having the tilt angle β[°] not equal to zero, β[°] being defined as φ giving the minimum value of retardation R[φ] which is retardation measured for incident light coming in a direction tilted by φ° from a normal line relative to the film-plane, the direction being in a plane including the direction perpendicular to the in-plane slow axis thereof and the normal line; and having retardation along the thickness direction at a wavelength of 550 nm, Rth(550), not equal to zero.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/567,054filed on Sep. 25, 2009, which claims benefit of priority under 35 U.S.C.119 to Japanese Patent Application Nos. 2008-247733, filed on Sep. 26,2008, and 2009-086914, filed on Mar. 31, 2009, which are expresslyincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a novel acryl-base polymer film usefulas optical members of liquid-crystal display devices, etc., to a noveloptical compensation film for IPS or FFS-mode liquid-crystal displaydevices, and to an IPS or FFS-mode liquid-crystal display device havingthe film.

2. Background Art

Heretofore, in-plane switching (IPS) mode and fringe-field switching(FFS) mode liquid-crystal display devices have been proposed, whereliquid-crystal molecules act to switch in a horizontal alignment staterelative to the substrate, and in fact, they have been put intopractical use. IPS-mode and FFS-mode liquid-crystal display devices areexcellent in the viewing angle characteristics but have a problem oflight leakage in oblique directions in the black state.

To overcome the problem of light leakage in oblique directions in theblack state, proposed is use of a cellulose acylate film satisfyingpredetermined optical characteristics, as a protective film for thepolarizing plate to be proposed between the liquid-crystal cell and thepolarizing element (JP-A 2006-227606). Also proposed is disposition of aC-plate and a biaxial film between the liquid-crystal cell and thepolarizing element (JP-A 2005-265889).

As an IPS-mode liquid-crystal display device having solved a problem ofvisibility failure owing to light leakage, color unevenness, color shiftand the like around frames, proposed are use of a protective film havingpredetermined optical characteristics for the protective film of thepolarizing plate to be disposed on the side of the liquid-crystal cell,and use of an acryl-base polymer film as one example of the protectivefilm (JP-A 2007-264534).

On the other hand, JP-A 2007-38646 proposes a method of producing anoptical film whose optical axis is inclined in the thickness directionby having a melt of thermoplastic polymer composition through the nipbetween two rolls running at a certain condition.

SUMMARY OF THE INVENTION

However, there is a demand for further advanced image quality in theart, and it is desired to further improve the display characteristics ofliquid-crystal display devices.

Accordingly, an object of the present invention is to provide a novelacryl-base polymer film and an optical compensation film capable ofsolving the problem of light leakage in oblique directions of IPS-mode,FFS-mode or the like horizontal alignment-mode liquid-crystal displaydevices in the black state, thereby contributing toward attaining moreideal black state.

Another object of the invention is to provide an IPS-mode, FFS-mode orthe like horizontal alignment-mode liquid-crystal display device capableof solving the problem of light leakage in oblique directions in theblack state and capable of attaining more ideal black state.

The means for achieving the objects are as follows.

[1] An optical compensation film for IPS or FFS-mode liquid crystaldisplay devices, having the tilt angle β[°] not equal to zero, β[°]being defined as φ giving the minimum value of retardation R[φ] which isretardation measured for incident light coming in a direction tilted byφ° from a normal line relative to the film-plane, the direction being ina plane including the direction perpendicular to the in-plane slow axisthereof and the normal line; and

having retardation along the thickness direction at a wavelength of 550nm, Rth(550), not equal to zero.

[2] The optical compensation film for IPS or FFS-mode liquid crystaldisplay devices of [1], having retardation in plane at a wavelength of550 nm, Re(550), of from −10 nm to 10 nm, and retardation along thethickness direction at the same wavelength, Rth(550), of from −30 nm to30 nm (provided that Rth(550)≠0).[3] The optical compensation film for IPS or FFS-mode liquid crystaldisplay devices of [1] or [2], of which the wavelength dispersioncharacteristics of Re, |Re(630)−Re(450)|, is equal to or less than 1.5nm, and the wavelength dispersion characteristics of Rth,|Rth(630)−Rth(450)|, is equal to or less than 4 nm.[4] The optical compensation film for IPS or FFS-mode liquid crystaldisplay devices of any one of [1]-[3], which is an acryl-base polymerfilm.[5] The optical compensation film for IPS or FFS-mode liquid crystaldisplay devices of [4], comprising as a major ingredient, an acryl-basepolymer having at least one unit selected from the group consisting oflactone ring unit, maleic anhydride unit, and glutaric anhydride unit.[6] The optical compensation film for IPS or FFS-mode liquid crystaldisplay devices of any one of [1]-[3], which comprises a cycloolefinpolymer-base film.[7] An acryl-base polymer film, having the tilt angle β[°] not equal tozero, β[°] being defined as φ giving the minimum value of retardationR[φ] which is retardation measured for incident light coming in adirection tilted by φ° from a normal line relative to the film-plane,the direction being in a plane including the direction perpendicular tothe in-plane slow axis thereof and the normal line; and

having retardation along the thickness direction at a wavelength of 550nm, Rth(550), not equal to zero, wherein

retardation in plane at a wavelength of 550 nm, Re(550), is from −10 nmto 10 nm;

retardation along the thickness direction at the same wavelength,Rth(550), is from −30 nm to 30 nm;

the wavelength dispersion characteristics of Re, |Re(630)−Re(450)|, isequal to or less than 1.5 nm; and

the wavelength dispersion characteristics of Rth, |Rth(630)−Rth(450)|,is equal to or less than 4 nm.

[8] An IPS or FFS-mode liquid crystal display device comprising:

a pair of substrates at least one of which has an electrode and whichare disposed to face each other, the electrode forming an electric fieldhaving a component parallel to the electrode-having substrate;

an alignment-controlled liquid-crystal layer disposed between the pairof substrates; and

a pair of polarizers disposed to sandwich the liquid-crystal layertherebetween;

wherein at least one of the pair of polarizers has at least one opticalcompensation film of any one of [1]-[6].

[9] An IPS or FFS-mode liquid crystal display device comprising:

a pair of substrates at least one of which has an electrode and whichare disposed to face each other, the electrode forming an electric fieldhaving a component parallel to the electrode-having substrate;

an alignment-controlled liquid-crystal layer disposed between the pairof substrates; and

a pair of polarizers disposed to sandwich the liquid-crystal layertherebetween;

wherein at least one of the pair of polarizers has at least one opticalcompensation film of any one of [7].

[10] An IPS or FFS-mode liquid-crystal display device comprising:

a pair of polarizing elements,

a liquid-crystal cell as horizontally aligned between the pair ofpolarizing elements, and

a film of any one of [1]-[7] individually between each of the pair ofpolarizing elements and the liquid-crystal cell.

[11] An IPS or FFS-mode liquid-crystal display device comprising:

a pair of polarizing elements, and

a horizontally liquid-crystal cell as horizontally aligned, disposedbetween the pair of polarizing elements,

a film of any one of [1]-[7] disposed between one of the pair ofpolarizing elements and the liquid-crystal cell, and

a cycloolefin-base polymer film disposed between the other of the pairof polarizing elements and the liquid-crystal cell.

[12] An IPS or FFS-mode liquid-crystal display device comprising:

a pair of polarizing elements,

a liquid-crystal cell as horizontally aligned, disposed between the pairof polarizing elements,

a film of any one of [1]-[7] disposed between one of the pair ofpolarizing elements and the liquid-crystal cell, and

an optically-biaxial film and a positive C-plate between the other ofthe pair of polarizing elements and the liquid-crystal cell.

According to the invention, it is possible to provide a novel acryl-basepolymer film and an optical compensation film capable of solving theproblem of light leakage in oblique directions of IPS-mode, FFS-mode orthe like horizontal alignment-mode liquid-crystal display devices in theblack state, thereby contributing toward attaining more ideal blackstate.

And according to the invention, it is also possible to provide anIPS-mode, FFS-mode or the like horizontal alignment-mode liquid-crystaldisplay device capable of solving the problem of light leakage inoblique directions in the black state and capable of attaining moreideal black state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of one example of an IPS-modeliquid-crystal display device of the invention.

FIG. 2 is a schematic cross-sectional view of another example of anIPS-mode liquid-crystal display device of the invention.

FIG. 3 is a schematic cross-sectional view of still another example ofan IPS-mode liquid-crystal display device of the invention.

FIG. 4 is a view for use in explaining the method for measuring thelevel of light leakage in Examples.

The meanings of the numerical references and signs in the drawings areas follows:

-   10 Polarizing element-   10 a Absorption axis-   12 Acryl-base polymer film (acryl-base polymer of the invention)-   14 Protective film-   14′ Protective film (biaxial film)-   12 a, 14 a, 14′ a, 16 a Slow axis-   16 Polymer film-   18 Positive C-plate-   a Rubbing axis in rubbing treatment applied to the substrate of    liquid-crystal cell-   LC-   LC IPS-mode liquid-crystal cell-   PL1 Polarizing plate on panel side-   PL2 Polarizing plate on backlight side

PREFERRED EMBODIMENT OF THE INVENTION

The present invention will be detailed below. Note that, in this patentspecification, any numerical expression in a style of “ . . . to.” willbe used to indicate a range including the lower and upper limitsrepresented by the numerals given before and after “to”, respectively.

In this description, Re and Rth are at a wavelength of 550 nm unlessotherwise specifically indicated. Also in this description, the range ofthe numerical data and the numerical range should be so interpreted asto indicate the numerical data and the numerical range that include theerror range generally acceptable for liquid-crystal display devices andtheir constitutive components. The same shall apply to the relationship(“parallel to”, “perpendicular to”, etc.) between optical axes(polarization axes of polarizing elements, slow axes ofoptically-anisotropic layers, etc.), and also to and the angle betweenthose axes.

1. Optical Compensation Film:

The invention relates to an optical compensation film for IPS-mode orFFS-mode liquid-crystal display devices having the tilt angle β[°] ofthe main axis not equal to zero, namely, β≠0, and having retardationalong the thickness direction at a wavelength of 550 nm, Rth(550), notequal to 0, namely, Rth(550)≠0. The optical compensation film of theinvention satisfies the above-mentioned predetermined opticalcharacteristics, therefore contributing toward solving the problem oflight leakage in oblique directions of IPS-mode, FFS-mode or the likehorizontal alignment-mode liquid-crystal display devices in the blackstate. More concretely, this is as described below. In an IPS-mode,FFS-mode or the like horizontal alignment-mode liquid-crystal displaydevice, the liquid-crystal molecules are horizontally aligned along thealignment control direction (generally the direction of the rubbingaxis) of the alignment film formed on the surface of the substrate in noapplication of driving voltage thereto, and in this condition,therefore, the device is in the black state. However, the device has apretilt angle in some degree, and in this, therefore, the liquid-crystalmolecules are not aligned completely horizontally. Accordingly, when thedisplay panel of the device is observed at oblique angles shifted in thevertical direction from the normal line direction, then asymmetric lightleakage may be caused by the asymmetricity of the alignment of theliquid-crystal molecules in the device. The optical compensation film ofthe invention satisfies the tilt angle β of the main axis, β≠0,therefore contributing toward solving the problem of the asymmetricityin light leakage in the black state to be caused by the pretilt angle ofan IPS-mode or FFS-mode liquid-crystal cell. As a result, even thoughsome light leakage occurs in an IPS-mode or FFS-mode liquid-crystaldisplay device in the black state, the degree of light leakage is nearlysymmetric in the vertical direction of the display panel, and thereforethe device can realize more ideal black state.

In the description, Re(λ) (unit: nm) and Rth(λ) (unit: nm) each indicateretardation in plane and retardation along the thickness direction of asample, an optically anisotropic layer, a film, a lamination or thelike, at a wavelength λ.

Re(λ) is measured by applying a light having a wavelength of λ nm in thenormal direction of the film, using KOBRA-21ADH or WR (by Oji ScientificInstruments).

The selectivity of the measurement wavelength λ nm may be conducted by amanual exchange of a wavelength-filter, a program conversion of ameasurement wavelength value or the like.

When a film to be tested is represented by an uniaxial or biaxialrefractive index ellipsoid, then its Rth(λ) is calculate according tothe method mentioned below.

With the in-plane slow axis (determined by KOBRA 21ADH or WR) taken asthe inclination axis (rotation axis) of the film (in case where the filmhas no slow axis, the rotation axis of the film may be in any in-planedirection of the film), Re(λ) of the film is measured at 6 points in allthereof, up to +50° relative to the normal direction of the film atintervals of 10°, by applying a light having a wavelength of λ nm fromthe inclined direction of the film.

With the in-plane slow axis from the normal direction taken as therotation axis thereof, when the film has a zero retardation value at acertain inclination angle, then the symbol of the retardation value ofthe film at an inclination angle larger than that inclination angle ischanged to a negative one, and then applied to KOBRA 21ADH or WR forcomputation.

With the slow axis taken as the inclination axis (rotation axis) (incase where the film has no slow axis, the rotation axis of the film maybe in any in-plane direction of the film), the retardation values of thefilm are measured in any inclined two directions; and based on the dataand the mean refractive index and the inputted film thickness, Rth maybe calculated according to the following formulae (A) and (B):

$\begin{matrix}{{{Re}(\theta)} = \begin{matrix}{\left\lbrack {{nx} - \frac{{ny} \times {nz}}{\sqrt{\begin{matrix}{\left\{ {{ny}\;{\sin\left( {\sin^{- 1}\left( \frac{\sin\left( {- \theta} \right)}{nx} \right)} \right)}} \right\}^{2} +} \\\left\{ {{nz}\;{\cos\left( {\sin^{- 1}\left( \frac{\sin\left( {- \theta} \right)}{nx} \right)} \right)}} \right\}^{\; 2}\end{matrix}}}} \right\rbrack \times} \\\frac{d}{\cos\left\{ {\sin^{- 1}\left( \frac{\sin\;\left( {- \theta} \right)}{nx} \right)} \right\}}\end{matrix}} & (A) \\{\mspace{79mu}{{Rth} = {\left\lbrack {\frac{{nx} + {ny}}{2} - {nz}} \right\rbrack \times d}}} & (B)\end{matrix}$

wherein Re(θ) means the retardation value of the film in the directioninclined by an angle θ from the normal direction; nx means the in-planerefractive index of the film in the slow axis direction; ny means thein-plane refractive index of the film in the direction vertical to nx;nz means the refractive index of the film vertical to nx and ny; and dis a thickness of the film.

When the film to be tested can not be represented by a monoaxial orbiaxial index ellipsoid, or that is, when the film does not have anoptical axis, then its Rth(λ) may be calculated according to the methodmentioned below.

With the in-plane slow axis (determined by KOBRA 21ADH or WR) taken asthe inclination axis (rotation axis) of the film, Re(λ) of the film ismeasured at 11 points in all thereof, from −50° to +50° relative to thenormal direction of the film at intervals of 10°, by applying a lighthaving a wavelength of λ nm from the inclined direction of the film.Based on the thus-determined retardation data of Re(λ), the meanrefractive index and the inputted film thickness, Rth(λ) of the film iscalculated with KOBRA 21ADH or WR.

The mean refractive index may be used values described in catalogs forvarious types of optical films. When the mean refractive index has notknown, it may be measured with Abbe refractometer. The mean refractiveindex for major optical film is described below: cellulose acetate(1.48), cycloolefin polymer (1.52), polycarbonate (1.59),polymethylmethacrylate (1.49), polystyrene (1.59).

The mean refractive index and the film thickness are inputted in KOBRA21ADH or WR, nx, ny and nz are calculated therewith. From thethus-calculated data of nx, ny and nz, Nz=(nx−nz)/(nx−ny) is furthercalculated.

In this description, Re, Rth and the refractive index are at awavelength of 550 nm unless otherwise specifically indicated for thewavelength for their measurement.

In this description, R[β] is the minimum value of the above-mentionedRe(θ), and β=θ.

From the viewpoint of solving the problem of the asymmetricity in lightleakage of an IPS-mode or FFS-mode liquid-crystal display device in theblack state, the tile angle β of the main axis of the opticalcompensation film of the invention is preferably |β|≦35°, morepreferably |β|≦30°.

Also from the viewpoint of solving the problem of the light leakage inoblique directions in the black state, the optical compensation film ofthe invention has Re(550) of preferably from −10 nm to 10 nm, orpreferably from −7 nm to 7 nm, even more preferably from −5 nm to 5 nm.From the same viewpoint, the optical compensation film of the inventionhas Rth(550) of preferably from −30 nm to 30 nm (but Rth(550)≠0), orepreferably from −20 nm to 20 nm, even more preferably from −15 nm to 15nm.

From the viewpoint of solving the problem of color shift in obliquedirections in the black state, the wavelength dispersion characteristicsof Re of the optical compensation film of the invention are preferably|Re(630)−Re(450)| of at most 1.5 nm, more preferably at most 1 nm. Fromthe same viewpoint, the wavelength dispersion characteristics of Rth ofthe optical compensation film of the invention are preferably|Rth(630)−Rth(450)| of at most 4 nm, more preferably at most 2 nm.

One embodiment of the optical compensation film of the invention is anacryl-base polymer film of which the tile angle β[°] of the main axis isβ≠0 and |β|≦45, and which has Re(550) of from −10 nm to 10 nm, Rth(550)of from −30 nm to 30 nm, wavelength dispersion characteristics of thein-plane retardation Re, |Re(630)−Re(450)| of at most 1.5 nm, andwavelength dispersion characteristics of the thickness-directionretardation Rth, |Rth(630)−Rth(450)| of at most 4 nm.

The thickness of the optical compensation film (e.g., acryl-base polymerfilm) just formed but unstretched is preferably from 20 μm to 200 μm,more preferably from 30 μm to 150 μm, even more preferably from 40 μm to100 μm.

Preferably, the thickness unevenness of the film is from 0% to 3% bothin the x-axis direction and in the y-axis direction, more preferablyfrom 0% to 2%, even more preferably from 0% to 1%.

The optical compensation film of the invention may be laminated with aC-plate or a biaxial film, in which the C-plate and the biaxial film mayhave a tilt angle. In this, β of the C-plate and the biaxial plate ispreferably |β|≦35°.

1.-1 Material of Optical Compensation Film:

One embodiment of the optical compensation film of the invention is anacryl-base polymer film containing, as the main ingredient thereof, atleast one polymer prepared through polymerization of at least onemonomer of acrylic acid, methacrylic acid or their derivatives(hereinafter this may be referred to as “(meth)acrylic acid monomer”)either singly or as combined with any other monomer (hereinafter thismay be referred to as “acryl-base polymer”). The derivatives of acrylicacid and methacrylic acid ((meth)acrylic acid) include methacrylates andacrylates. The methacrylates include cyclohexyl methacrylate,t-butylcyclohexyl methacrylate, methyl methacrylate, etc. The acrylatesinclude methyl acrylate, ethyl acrylate, butyl acrylate, isopropylacrylate, 2-ethylhexyl acrylate, etc.

Examples of other (meth)acrylic acid derivative include the compoundsrepresented by formula (1).

In the formula, R¹ and R² each independently respect a hydrogen atom orC₁₋₂₀ organic group. Examples of the C₁₋₂₀ organic group include linear,branched or cyclic C₁₋₂₀ alkyls.

Examples of the (meta)acryl-base monomer, which can be used as amaterial of the acryl-base polymer used for preparing the opticalcompensation film, include methyl(meth)acrylate, ethyl(meth)acrylate,n-propyl(meth)acrylate, n-butyl(meth)acrylate, tert-butyl(meth)acrylate,n-hexyl(meth)acrylate, 2-chloroethyl(meth)acrylate,2-hydroxyethyl(meth)acrylate, 3-hydroxypropyl(meth)acrylate,2,3,4,5,6-pentahydroxyethyl(meth)acrylate, and2,3,4,5-tetrahydroxypentyl(meth)acrylate. In terms of the thermalstability, preferably, methyl(meth)acrylate (referred to as “MMA”hereinunder) is at least used.

The acryl-base polymer to be used as a material of the opticalcompensation film of the invention may be a homopolymer or co-polymer.In terms of increasing the glass-transition temperature (referred to as“Tg hereinunder), the copolymers of any (meth)aryl-base monomer andanother polymerizable monomer are preferable.

Examples of another polymerizable monomer to be used in combination ofany (meth)aryl-base monomer for preparing the acyl-base polymer includearomatic vinyl compounds such as styrene, alkyl-substituted styrenes(such as o-methyl styrene, p-methyl styrene, 2,4-dimethyl styrene,o-ethyl styrene, p-ethyl styrene and p-tert-butyl styrene) andα-alkyl-substituted styrenes (such as α-methyl styrene andα-methyl-p-methyl styrene); cyanidation vinyl compounds acrylonitrileand methacrylonitrile; maleimides such as N-phenyl maleimide andN-cyclohexyl maleimide; unsaturated carboxylic acid anhydrides such aslactone ring unit, glutaric acid anhydride unit and maleic acidanhydride; unsaturated acids such as maleic acid; and glutarimide unit.Among these, in terms of the heat resistance, N-substituted maleimidessuch as N-phenyl maleimide, N-cyclohexyl maleimide and N-methylmaleimide; lactone ring unit, glutaric acid anhydride unit, maleic acidanhydride unit and glutarimide unit are preferable; and in terms of thehigh Tg, lactone ting unit, maleic acid unit and glutaric acid unit arepreferable.

Lactone Ring Unit:

Having the lactone ring unit in the molecular chain thereof (or the mainchain thereof if it is introduced into the main skeleton thereof), thecopolymer, the acryl-base polymer, may show high heat resistance andhave a high Tg, which is preferable. In terms of reducing bubbles andsilver streak, the cyclization-condensation reactivity to give a lactonering structure is preferably high sufficiently.

Examples of the lactone ring unit which can be used in the inventioninclude, but are not limited to, those described in JP-A-2007-297615,2007-63541, 2007-70607, 2007-100044, 2007-254726, 2007-254727,2007-261265, 2007-293272, 2007-297619, 2007-316366, 2008-9378 and2008-76764. They may be used alone respectively or in combination withothers.

The lactone ring in the main chain is preferably 4- to 8-membered ring.In terms of stability of the structure, 5- or 6-membered rings arepreferable, and 6-membered rings are more preferable. Examples of the6-membered lactone ring unit in the main chain include the structuresrepresented by formula (2) shown below and those described inJP-A-2004-168882. In terms of obtaining the high degrees ofpolymerization in preparing the polymers before being subjected tointroduction of the lactone ring in the main chain, obtaining easily thehigh productivity of polymers having the lactone ring unit in a highratio, and obtaining the good copolymerization of (meth)acrylates suchas methyl methacrylate, the lactone ring unit represented by formula (2)is preferable.

In formula (2), R¹¹ to R¹³ each independently represent a hydrogen atomor C₁₋₂₀ organic group.

There is no limitation on the C₁₋₂₀ organic group, and examples of theC₁₋₂₀ organic group include linear or branched alkyl, linear or branchedalkylenes, aryls, —OAc and —CN. The C₁₋₂₀ organic group may have anoxygen atom. The number of the carbon atoms in each of R¹¹ to R¹³ ispreferably from 1 to 10, and more preferably from 1 to 5.

The acryl-base polymer having a lactone ring unit may be preparedaccording to any process. One preferable example of the process is asfollows. A polymer, having a hydroxy and an ester, is prepared accordingto any polymerization step, and, after that, is subjected to a heattreatment to form a lactone ring unit therein.

Maleic Acid Anhydride Unit:

Having the maleic acid anhydride unit in the molecular chain thereof (orthe main chain thereof if it is introduced into the main skeletonthereof), the copolymer, the acryl-base polymer, may show high heatresistance and have a high Tg, which is preferable.

There is no limitation on the maleic acid anhydride unit which can beused in the invention. Examples of the maleic acid anhydride includethose described in JP-A-2007-113109, 2003-292714, 6-279546, 2007-51233,2001-270905, 2002-167694, 2000-302988, 2007-113110 and 2007-11565; andmaleic acid-base modified polymers. Among these, the polymers describedin JP-A-2007-113109 and maleic acid modified MAS polymers (methylmethacrylate-acrylonitrile-styrene copolymers) such as “DEL PET 980N” byASAHI CHEMICALS are preferable. These may be used alone respectively orin combination with the other(s). The acryl-base polymer having a maleicacid unit may be prepared according to any process.

There is no limitation on the acryl-base polymers having the maleic acidunit. Examples of the acryl-base polymers having the maleic acid include(anhydride) maleic acid modified MA polymers, (anhydride) maleic acidmodified MAS polymers (methyl methacrylate-acrylonitrile-styrenecopolymers), (anhydride) maleic acid modified MBS polymers, (anhydride)maleic acid modified AS polymers, (anhydride) maleic acid modified AApolymers, (anhydride) maleic acid modified ABS polymers, ethylene-maleicacid anhydride copolymers, ethylene-(meth)acrylate-maleic acid anhydridecopolymers and maleic acid anhydride grafted poly propylene.

Examples of the maleic acid anhydride unit include the group representedby formula (3).

In formula (3), R²¹ and R²² each independently represent a hydrogen atomor C₁₋₂₀ organic group.

There is no limitation on the C₁₋₂₀ organic group, and examples of theC₁₋₂₀ organic group include linear or branched alkyl, linear or branchedalkylenes, aryls, —OAc and —CN. The C₁₋₂₀ organic group may have anoxygen atom. The number of the carbon atoms in each of R²¹ and R²² ispreferably from 1 to 10, and more preferably from 1 to 5.

In terms of controlling intrinsic birefringence, when R²¹ and R²²contains hydrogen atom(s) therein respectively, the polymer preferablycontains further unit derived from any other monomer(s). Examples ofsuch acryl-base polymers, having units derived from the three or moremonomers, include methyl-methacrylate-maleic acid anhydride-styrenecopolymers.

Glutaric Acid Anhydride Unit:

Having the glutaric acid anhydride unit in the molecular chain thereof(or the main chain thereof if it is introduced into the main skeletonthereof), the copolymer, the acryl-base polymer, may show high heatresistance and have a high Tg, which is preferable.

There is no limitation on the glutaric acid anhydride unit which can beused in the invention. Examples of the glutaric acid anhydride unitinclude those described in JP-A-2006-241263, 2004-70290, 2004-70296,2004-126546, 2004-163924, 2004-291302, 2004-292812, 2005-314534,2005-326613, 2005-331728, 2006-131898, 2006-134872, 2006-206881,2006-241197, 2006-283013, 2007-118266, 2007-176982, 2007-178504,2007-197703, 2008-74918 and WO 2005/105918. Among these, those describedin JP-A-2008-74918 are preferable. These may be used alone respectivelyor in combination with the other(s).

Examples of the glutaric acid anhydride unit include the grouprepresented by formula (4).

In formula (3), R³¹ and R³² each independently represent a hydrogen atomor C₁₋₁₀ organic group.

The number of carbon atoms in each of R³¹ and R³² is preferably from 1to 10, and more preferably from 1 to 10.

The acryl-base polymer having a glutaric acid anhydride unit may beprepared according to any process. One preferable example of the processis as follows. Copolymerization of unsaturated carboxylic acid anhydridemonomer, which gives a glutaric acid anhydride unit, and alkylunsaturated carboxylate monomer is carried out to form a copolymer.After that, the copolymer is subjected to a dialcohol or dehydrationreaction under heat in the presence or in the absence of catalyst, tothereby allow an intramolecular cyclization.

Other Co-Polymerizable Ingredient(s):

The acryl-base polymer may contain other unit(s) derived from themonomer(s) capable of copolymerization in the amount as not losing theheat-resistance. Examples of the other monomer capable ofcopolymerization include aromatic vinyl compounds such as styrene,α-methyl styrene, o-methyl styrene, p-methyl styrene, o-ethyl styrene,p-ethyl styrene and p-t-butyl styrene; cyanidation vinyl compoundsacrylonitrile, methacrylonitrile and ethacrylonitrile; Acryl glycidylether, styrene-p-glycidyl ether, p-glycidyl styrene, itaconic acidanhydride, N-methyl maleimide, N-ethyl maleimide, N-cyclohexylmaleimide, N-phenyl maleimide, acrylamide, methacrylamide, N-methylacrylamide, butoxymethyl acrylamide, N-propyl methacrylamide, aminoethylacrylate, propyl aminoethyl acrylate, dimethyl aminoethyl methacrylate,ethyl aminopropyl methacrylate, phenyl aminoethyl methacrylate,cyclohexyl aminoethyl methacrylate, N-vinyl diethylamine, N-acetyl vinylamine, allyl amine, methallyl amine, N-methyl allylamine, p-aminostyrene, 2-isopropenyl-oxazoline, 2-vinyl-oxazoline, 2-acroyl-oxazoline,2-styryl-oxazoline, nitrile-base monomers such as acrylonitrile; vinylesters such as vinyl acetate; and glutarimide units.

Preferable examples of the acryl-base polymer include acryl-basepolymers having at least one unit selected from the group consisting ofa lactone unit, maleic anhydride unit and glutaric anhydride unit alongwith the repeated unit derived from (meth)acrylic acid ester. Morepreferable examples of the acryl-base polymer include acryl-basepolymers having at least one unit selected from the group consisting ofa lactone unit or maleic anhydride unit along with the repeated unitderived from (meth)acrylic acid ester.

The acryl-base polymer preferably contains the MMA unit (monomer) in theamount of 30% or more by mole, and more preferably from 30 to 80% bymole. The acryl-base polymer preferably contains at least one unitselected from the group consisting of a lactone unit, maleic anhydrideunit and glutaric anhydride unit along with the repeated unit of MMA.The ratio of at least one unit selected from the group consisting of alactone unit, maleic anhydride unit and glutaric anhydride unit ispreferably from 5 to 60% by mole, and more preferably from 10 to 50% bymole, with respect to the total moles of all monomers in the acryl-basepolymer.

The Tg of the acryl-base polymer is preferably from 105 to 170 degreesCelsius, more preferably from 110 to 160 degrees Celsius, and much morepreferably from 115 to 150 degrees Celsius. The melt viscosity of theacryl-base polymer is preferably from 500 Pa·s to 10000 Pa·s, morepreferably from 800 Pa·s to 7000 Pa·s, much more preferably from 800Pa·s to 7000 Pa·s, and even much more preferably from 1000 Pa·s to 5000Pa·s, at 230 degrees Celsius under being applied 1% distortion with 1Hz.

The weight-averaged molecular weight of the acryl-base polymer ispreferably from 1,000 to 2,000,000, more preferably from 5,000 to1,000,000, much more preferably from 10,000 to 500,000, and even muchmore preferably from 50,000 to 500,000.

The optical compensation film of the invention may be formed of apolymer film containing a thermoplastic polymer as a main ingredientother than the acryl-base polymer film. Examples of the thermoplasticpolymer include cycloolefin-base polymers, cellulose acylates,polyesters and polycarbonates. When the film is prepared according to amelt-extrusion method, the material may be selected form the materialsshowing good film-forming properties for the melt-extrusion method, andin this regard, cycloolefin-base polymers and cellulose acylates arepreferable. These thermoplastic polymers may be used alone respectivelyor in combination with the other polymer(s). Among these, celluloseacylates and cycloolefin-base polymers which are prepared according toan addition polymerization are preferable. In the description, the term“cellulose acylate-base film” is used for any films containing at leastone cellulose acylate as a main ingredient; and the term“cycloolefin-base polymer” is used for any films containing at least onecycloolefin base polymer (copolymer or homopolymer) as a mainingredient.

Examples of the cycloolefin-base copolymer include norbornene-basepolymers. They may be prepared according to a ring-openingpolymerization or addition polymerization.

Examples of the addition polymerization or the polymers obtained by themethod include those described in Japanese patent Nos. 3517471, 3559360,3867178, 3871721, 3907908 and 3945598; JP-A-2005-527696, 2006-28993, and2006-11361; and WO2006-/004376 and WO2006-/030797. Among these, thosedescribed in Japanese patent No. 3517471 are preferable.

Examples of the ring-opening polymerization or the polymers obtained bythe method include those described in WO98/14499, Japanese patent Nos.3060532, 3220478, 3273046, 3404027, 3428176, 3687231, 3873934 and3912159. Among these, those described in WO98/14499 and Japanese patentNo. 3060532 are preferable.

Among the cycloolefin-base polymers, those obtained according to anaddition polymerization are preferable. Any commercially availablepolymers may be used; and examples of the polymer include “TOPAS #6013”(by Polyplastics) which may prevent gel from occurring in the extrusionstep.

Examples of the cellulose acylate include any cellulose acylate in whichthree hydroxys in a cellulose unit are at least partially replaced withan acyl. The acyl is preferably a C₃₋₂₂ acyl, and may be an aliphatic oraromatic acyl. Among these, cellulose acylates having an aliphatic acylare preferable; cellulose acylates having a C₃₋₇ aliphatic acyl are morepreferable; and cellulose acylates having s C₃₋₆ acyl are much morepreferable. The cellulose acylate may have plural acyls in eachmolecule. Preferable examples of the acyl include acetyl, propionyl,butyryl, pentanoyl and hexanoyl. Among these, more preferable are anycellulose acylates having one or more selected from the group consistingof acetyl, propionyl and butyryl; and much more preferable are anycellulose acylates having both of acetyl and propionyl, referred to asCAP. CAP can be easily prepared, and is stable during the extrusionstep.

The optical compensation film of the invention contains at least oneadditive along with the main ingredient, polymer material such asacryl-base polymer. Examples of the additive which can be used in theinvention include plasticizers, stabilizers, mat agents, UV absorbingagents, IR absorbing agents and retardation controlling agents. When thefilm is prepared according to a melt-extrusion process, the additive maybe added anytime in the process. For example, it may be added to thefilm finally in the process

The additives which can be used in the invention ill be described indetail.

Stabilizer:

The optical compensation film of the invention may contain at least onestabilizer. The stabilizer is effective for antioxidation offilm-constituting ingredients, for trapping the acids formed throughdecomposition, and for retarding or inhibiting the radical group-causeddecomposition under light or heat. The stabilizer is effective forinhibiting degradation such as discoloration or molecular weightreduction to be caused by various types of decompositions includingdecomposition not as yet clarified, and also inhibiting formation ofvolatile ingredients. Preferably, the stabilizer is added before orduring hot melting of thermoplastic polymer. The stabilizer is requiredto be still effective to exhibit its function, without being decomposedat the polymer melting temperature at which the polymer is formed into afilm.

Typical example of the stabilizer includes phenol-type stabilizers,phosphite-type stabilizers, thioether-type stabilizers, amine-typestabilizers, epoxy-type stabilizers, lactone-type stabilizers,amine-type stabilizers, metal inactivators (tin-type stabilizers), etc.These are described in JP-A 3-199201, 5-1907073, 5-194789, 5-271471, and6-107854. Preferably, at lest one of phenol-type and phosphite-typestabilizers is used in the invention.

One or more of the above-mentioned stabilizers may be used herein eithersingly or as combined. Not detracting from the object of the invention,the amount of the stabilizer to be in the film may be suitablydetermined. Preferably, the amount of the stabilizer to be added is from0.001 to 5% by mass relative to the mass of the thermoplastic polymer,more preferably from 0.005 to 3% by mass, even more preferably from 0.01to 0.8% by mass.

Preferable examples of the stabilizer include phenol-type stabilizers.Phenol-type stabilizers may be used for stabilizing the polymer materialduring the thermal melting. Exampled of the phenol-type stabilizerinclude 2,6-dialkyl phenol derivatives as described in U.S. Pat. No.4,839,405, 12-14 columns. More preferred are those having a molecularweight of at least 500. Preferred phenol-type stabilizers includehindered phenol-type stabilizers. These materials are readily availableas commercial products, and are sold, for example, by the followingmanufacturers. Ciba Specialty Chemicals provides commercial products ofIrganox 1076, Irganox 1010, Irganox 3113, Irganox 245, Irganox 1135,Irganox 1330, Irganox 259, Irganox 565, Irganox 1035, Irganox 1098,Irganox 1425WL. Asahi Denka Kogyo provides commercial products ofAdekastab AO-50, Adekastab AO-60, Adekastab AO-20, Adekastab AO-70,Adekastab AO-80. Sumitomo Chemical provides commercial productsSumilizer BP-76, Sumilizer BP-101, Sumilizer GA-80. Shipro Chemicalprovides commercial products Seenox 326M, Seenox 336B.

As phosphite-type stabilizers, more preferred are the compoundsdescribed in JP-A 2004-182979, paragraphs [0023]-[0039]. Specificexamples of phosphite-type stabilizers include compounds described inJP-A 51-70316, 10-306175, 57-78431, 54-157159, 55-13765. As otherstabilizers, preferred are the materials described in detail in HatsumeiKyokai Disclosure Bulletin (No. 2001-1745, issued on Mar. 15, 2001, byHatsumei Kyokai), pp. 17-22.

The phosphite-type stabilizers are preferably high-molecular ones forsecuring the stability thereof at high temperatures, having a molecularweight of at least 500, more preferably at least 550, even morepreferably at least 600. Also preferably, the stabilizers have anaromatic ester group as at least one substituent therein. Alsopreferably, the phosphite-type stabilizers are triesters, morepreferably not mixed with impurities of phosphoric acid, monoester ordiester. In case where the stabilizer contains such impurities,preferably, the content of the impurities is at most 5% by mass, morepreferably at most 3% by mass, even more preferably at most 2% by mass.For the stabilizers of the type, usable are the compounds described inJP-A 2004-182979, [0023] to [0039], and also usable are the compoundsdescribed in JP-A 51-70316, 10-306175, 57-78431, 54-157159, and55-13765. Preferred examples of phosphite-type stabilizers are mentionedbelow. However, the phosphite-type stabilizers for use in the inventionshould not be limited to these.

Asahi Denka provides commercial products of Adekastab 1178, 2112, PEP-8,PEP-24G, PEP-36G, HP-10; and Clariant provides commercial products ofSandostab P-EPQ.

Also preferred for use herein are stabilizers having both phenol andphosphite moieties in one molecule. The compounds are described indetail in JP-A 10-273494, and their examples are, but not limitedthereto, within the scope of the examples of the stabilizers mentionedin the above. Typically, Sumitomo Chemical provides commercial productsof Sumilizer GP.

Preferable examples of the stabilizer include thioether-basestabilizers. The molecular weight of the thioether-base stabilizer ispreferably equal to or more than 500. Any known thioether-basestabilizers can be used. They are commercially available as SumitomoChemical's products of Sumilizer TPL, TPM, TPS, TDP. Asahi Denka Kogyoprovides commercial products of Adekastab AO-4125.

Preferable examples of the stabilizer include epoxy-base stabilizers.The epoxy-base stabilizer is preferably selected form the compoundshaving an aliphatic, aromatic, alicyclic, aromatic-aliphatic, orheterocyclic structure and the side chains thereof having an epoxy. Theepoxy group may connect to the residue of any molecule via an ether orester bond as a glycidyl, or exist as a moiety of N-glycidyl derivativessuch as heterocyclic amine, amide or imide. Such epoxy compounds arecommercially available. Examples of the compound are described inJP-A-11-189706, [0096] to [0112]. Such epoxy compounds are available asproducts of Adekastab O-130P and O-180A (by Asahi Denka Kogyo).

Preferable examples of the stabilizer include tin-base stabilizers. Anyknown tin-base stabilizer can be used. Preferable examples of thetin-base stabilizer include octyl thin maleate polymers, monostearylthin tris(isooctylthioglycolate) and dibutyl thin dilaurate.

In the description, the term “stabilizer” means a concept encompassingany acid-trapping agents and any light stabilizers. The stabilizer(s)capable of mainly trapping any acid, acid-trapping agent(s), thestabilizer(s) capable of mainly improving the light stabilization, lightstabilizer(s), or other stabilizer(s) may be used. Among these,phenol-base stabilizers capable of trapping radicals are preferable.

Acid-Trapping Agent:

The decomposition of the materials in the acryl-base polymers may bepromoted by acid under the high temperature, and therefore, anacid-trapping agent is preferably added to the film.

The acid-trapping agent is a gent capable of achieving inactivation ofthe acid via reaction with the acid; and there is no limitation on theacid-trapping agent. Preferable examples of the acid-trapping agentinclude epoxy compounds described in U.S. Pat. No. 4,137,201. Such epoxycompounds are known as an acid-trapping agent in the technical field.Examples of the epoxy compound include diglycidyl ethers of variouspolyglycols such as diglycidyl ethers of glycerol or polyglycol whichare derived by condensation of one mole of glycol and about 8-40 molesof ethylene oxide; metal epoxy compounds which have been used along withvinyl chloride polymers; condensation products of epoxidation ethers;diglycidyl ethers of bisphenol A (or, that is, 4,4′-dihydroxy diphenyldimethyl ethane); esters of epoxidation unsaturated aliphatic acids suchas C₂₋₄ alkyl esters of C₂₋₂₂ aliphatic acids (for example, butyl epoxystearate); and triglycerides of various epoxidation long-chain aliphaticacids such as epoxidation plant oil and other unsaturated natural oil(one of their typical examples is epoxidation soy oil, they may bereferred to as epoxidation natural triglycerides or unsaturated naturalacids, and these aliphatic acids may have 12-22 of carbon atoms.

“EPON 815c”, which is a commercially available epoxy resin having epoxygroups, and condensation products of epoxidation ether oligomers areespecially preferable.

Examples of the acid-trapping agent other than those described aboveinclude oxetane compounds, oxazoline compounds, alkali earth salts oforganic acids; alkali earth acetylacetonate complexes; and thosedescribed in JP-A-194788, paragraphs 68-105.

The acid-trapping agent may be called as other names such as anacid-capturing agent, acid scavenger or the like, but any agents may beused in the invention regardless of the name.

The amount of the acid-trapping agent is preferably from 0.001% by massto 5% by mass, more preferably from 0.005 to 3% by mass, and much morepreferably from 0.01 to 2% by mass with respect to the mass of thepolymer material.

Light Stabilizer:

The optical compensation film (for example, acryl-base polymer film) ofthe invention may contain at least one light stabilizer. Examples of thelight stabilizer include hindered amine light stabilizer (HALS). Andspecific examples thereof include 2,2,6,6-tetrakis alkyl piperidinecompounds, acid-adducts thereof, and metal complexes thereof; which aredescribed in U.S. Pat. No. 4,619,956, columns 5-11, and U.S. Pat. No.4,839,405, columns 3-5. Theses are commercially available as Asahi DenkaKogyo's products such as Adekastab LA-57, LA-52, LA-67, LA-62 and LA-77or as Chiba Specialty Chemicals's products such as TINUVIN 765 and 144.

These hindered amine light stabilizers may be used alone respectively orin combination with other(s). The hindered amine light stabilizer may beused along with other additive(s) such as plasticizer, acid-trappingagent and UV absorbing agent. Or the additive having a residue of thehindered amine light stabilizer therein may be also used. The amount ofthe light stabilizer is preferably from 0.01 to 20 parts by mass, morepreferably from 0.02 to 15 parts by mass and much more preferably from0.05 to 10 parts by mass with respect to 100 parts of the polymermaterial.

UV Absorbing Agent:

The optical compensation film (for example, acryl-base polymer film) ofthe invention may contain one or more UV absorbing agent. In terms ofthe durability, the compounds capable of almost absorbing UV lighthaving a wavelength not longer than 380 nm are preferable; and in termsof displaying quality, the compounds capable of hardly absorbing UVlight having a wavelength not shorter than 400 nm are preferable.Examples of the UV absorbent include oxybenzophenone compounds,benzotriazole compounds, salicylate compounds, benzophenone compounds,cyanoacrylate compounds, and nickel complex compounds; and preferred arebenzotriazole compounds and benzophenone compounds. Among theses,especially, preferred are benzotriazole compounds causing littlecoloration. Preferable examples of these UV absorbing agents includethose described in JP-A-60-235852, 3-199201, 5-1907073, 5-194789,5-271471, 6-107854, 6-118233, 6-148430, 7-11056, 7-11055, 7-11056,8-29619, 8-239509, and 2000-204173. The amount of the UV absorbing agentis preferably 0.01 to 2% by mass, and more preferably from 0.01 to 1.5%by mass with respect to the mass of the melt to be used for preparingthe film.

As the UV absorbing agent which can be used in the invention, polymerscapable of absorbing UV light described in JP-A-6-148430 and anypolymers containing UV absorbing monomers. The weight-averaged molecularweight of the polymer derived from the UV absorbing monomer ispreferably from 2000 to 30000, and more preferably from 5000 to 20000.

The ratio of the UV absorbing monomer in the polymer is preferably from1 to 70% by mass and more preferably from 5 to 60% by mass.

Examples of the commercially available UV absorbing monomer include1-(2-benzotriazole)-2-hydroxy-5-(2-vinyloxy carbonyl ethyl)benzene,RUVA-93 by Otsuka Chemical Co. ltd., which is1-(2-benzotriazole)-2-hydroxy-5-(2-methacryloyloxy ethyl)benzene, andanalogous compounds thereof. Any homopolymers of these monomers and anycopolymers of the monomers and the other monomers may be preferablyused. Examples of the commercially available UV absorbing polymerinclude PUVA-30M by Otsuka Chemical Co. ltd. The UV absorbing agent maybe used alone respectively or in combination with other(s).

Examples of the commercially available UV absorbing agent are asfollows:

As an benzotriazole-base agent, TINUBIN P (byChiba-Specialty-Chemicals), TINUBIN 234 (by Chiba-Specialty-Chemicals),TINUBIN 320 (by Chiba-Specialty-Chemicals), TINUBIN 326 (byChiba-Specialty-Chemicals), TINUBIN 327 (by Chiba-Specialty-Chemicals),TINUBIN 328 (by Chiba-Specialty-Chemicals), Sumisorbe 340 (by SumitomoChemical) and Adekastabe LA-31 (by Asahi Denka Kogyo) are exemplified.As a benzophenone-base UV absorbing agent, SEESORBE 100 (by SHIPRO KASEIKAISHA LTD.), SEESORBE 101 (by SHIPRO KASEI KAISHA LTD.), SEESORBE 101S(by SHIPRO KASEI KAISHA LTD.), SEESORBE 102 (by SHIPRO KASEI KAISHALTD.), SEESORBE 103 (by SHIPRO KASEI KAISHA LTD.), Adekastabe LA-51 (byAsahi Denka Kogyo), CHEMISORPE111 (by CHEMIPRO KASEI KAISHA ltd.) andUVINUL D-49 (by BASF) are exemplified. As a salicylic acid-base UVabsorbing agent, SEESORBE 201 (by SHIPRO KASEI KAISHA LTD.) and SEESORBE201 (by SHIPRO KASEI KAISHA LTD.) are exemplified. As cyanoacrylate-base UV absorbing agent, SEESORBE 501 (by SHIPRO KASEI KAISHALTD.) and UVINUL N-539 (by BASF) are exemplified.

The preferable range of the amount of the UV absorbing agent or the UVabsorbing polymer may be varied depending on the types or conditions inuse of the material. Generally, the amount of the UV absorbing agent ispreferably from 0.2 to 3.0 g per 1 m² of the film, more preferably from0.4 to 2.0 g per 1 m² of the film, and much more preferably from 0.5 to1.5 per 1 m² of the film. The amount of the UV absorbing polymer ispreferably from 0.6 to 9.0 g per 1 m² of the film, more preferably from1.2 to 6.0 g per 1 m² of the film, and much more preferably from 1.5 to3.0 per 1 m² of the film.

Plasticizer:

The optical compensation film (for example, acryl-base polymer film) ofthe invention may contain a plasticizer. Adding a plasticizer to thefilm is favorable from the viewpoint of film reformation, for example,for improving the mechanical properties of the film, impartingflexibility to the film, imparting water absorbability to the film orreducing the moisture permeability of the film. In case where the filmof the invention is produced according to a melt formation method, aplasticizer may be added to the film for the purpose of depressing themelting temperature of the film-constituting material throughplasticizer addition thereto, than the glass transition temperature ofthe thermoplastic polymer used, or for the purpose of reducing theviscosity of the polymer composition at the same heating temperaturethan that of the thermoplastic polymer to which the plasticizer is notadded.

For example, for the film of the invention, preferably used areplasticizers selected from phosphate ester-type plasticizers, phthalicacid ester-type plasticizers, trimellic acid ester-type plasticizers,pyromellic ester type plasticizers, polyfunctional alcohol ester-typeplasticizers, glycolate-type plasticizers, citric acid ester-typeplasticizers, fatty aid ester-type plasticizers, carboxylic acidester-type plasticizers, and polyester-type plasticizers. Preferable arestabilizers other than phosphate ester-type plasticizers such aspolyfunctional alcohol ester-type plasticizers, polyester-typeplasticizers, citric acid ester-type plasticizers and phthalic acidester-type plasticizers. In addition, also preferably used are polymersproduced through polymerization of ethylenic unsaturated monomers andhaving a weight-average molecular weight of from 500 to 10000, as inJP-A 2003-12859, as well as acrylic polymers, acrylic polymers having anaromatic ring in the side branches, and acrylic polymers having acyclohexyl group in the side branches.

The plasticizer may be liquid or solid, and colorless plasticizers arepreferable. Preferably, the plasticizer is thermally stable at a hightemperature, and the temperature of starting decomposition of the agentis preferably equal to or higher than 150 degrees Celsius, and morepreferably equal to or higher than 200 degrees Celsius. The amount ofthe agent may be decided so that any undesired effect is not made on theoptical properties and mechanical properties. The amount is preferablyfrom 0.001 to 50 parts by mass, and more preferably from 0.01 to 30parts by mass with respect to 100 parts by mass of the polymer material.The amount of from 0.1 to 15% by mass is especially preferable.

Examples of the plasticizer include phosphate ester-type stabilizerssuch as cycloalkyl phosphates and aryl phosphates. The substitutionstherein may be same or different from each other, and the substitutionmay have at least one substituent. The stabilizers of the mixtures ofphosphates having alkyl, cycloalkyl and aryl may be used. Thesubstituents may connect each other to form a ring. Examples of thephosphate ester-type stabilizer include alkylene bis(dialkyl phosphate)such as ethylene bis(dimethyl phosphate) and butylene bis(diethylphosphate); alkylene bis(diaryl phosphate) such as ethylene bis(diphenylphosphate) and propylene bis(dinaphthyl phosphate); arylene bis(dialkylphosphate) such as phenylene bis(dibutyl phosphate) and bisphenylenebis(dioctyl phosphate); and arylene bis(diaryl phosphate) such asphenylene bis(diphenyl phosphate) and naphthylene bis(ditoluoylphosphate). The substitutions therein may be same or different from eachother, and the substitution may have at least one substituent. Thestabilizers of the mixtures of phosphates having alkyl, cycloalkyl andaryl may be used. The substituents may connect each other to form aring.

Furthermore, any polymers having the phosphate ester moiety thereinpartially or regularly may be used, and the moiety may be introduced inthe molecular of the other additive(s) such as an antioxidant,acid-trapping agent and UV absorbing agent. Among the compounds describeabove, aryl phosphates and arylene bis(diaryl phosphate) are preferable.More specifically, triphenyl phosphate and phenylene bis(diphenylphosphate) are preferable. and the phosphate ester-type plasticizersdescribed in JP-A-6-501040 are also preferable. And the phosphateester-type plasticizers, hardly volatilizing, described inJP-A-2002-363423, [0027]-[0034], JP-A-2002-265800, [0027]-[0034] andJP-A-2003-155292, [0014]-[0040], are also exemplified.

Examples of the commercially available phosphate ester-type plasticizerinclude, but are not limited to, Adekastab FP-500, FP-600, FP-700FP-2100 and PFR (by Asahi Denka Kogyo); and Reoforce BAPP (byAjinomoto).

As the polyfunctional ester plasticizer, polyester plasticizer andpolymer plasticizer, those described in JP-A-2007-231157, [0086]-[0138],can be used, and they may be used alone respectively or in combinationwith the other(s).

According to the invention, saccharide plasticizers are also preferable.The saccharide plasticizer may be selected from monosaccharides orpolysaccharides containing 2-10 of monosaccharide units; and the featurethereof resides in that the substitutable group(s) therein such ashydroxy, carboxyl, amino or mercapto is replaces with substituentgroup(s). Examples of the substituent group include an ether group,ester group, amido group and imido group. Examples of the monosaccharideand the polysaccharide, containing 2-10 of monosaccharide units, includeerythritol, trehalose, ribose, arabinose, xylose, lyxose, arose,altrose, glucose, fructose, mannose, gulose, idose, galactose, talose,trehalose, isotrehalose, neotrehalose, trehalosamine, Kojic biose,nigerose, maltose, maltitol, isomaltose, sophorose, laminaribiose,cellobiose, α-cyclodextrine, β-cyclodextrine, γ-cyclodextrine,δ-cyclodextrine, xylitol and sorbitol.

According to the invention, polymer plasticizers are preferable.Examples of the polymer plasticizer include alicyclic hydrocarbon-basepolymers, acryl-base polymers such as poly methyl acrylates and polymethyl methacrylates; vinyl-base polymers such as poly vinyl isobutylether and poly N-vinyl pyrolidone; styrene-base polymers such aspolystyrene and poly 4-hydroxy styrene; polyesters such as poly butylenesuccinate, poly ethylene terephthalate and poly ethylene naphthalate;poly ethers such as polyethylene oxide and polypropylene oxide;polyamides; polyurethanes; and polyureas. The number-averaged molecularweight of the polymer is preferably from about 1,000 to about 500,000,and more preferably from about 5,000 to about 200,000. When themolecular weight is equal to or less than 1,000, the volatilization mayoccur; on the other hand, when the molecular weight is more than500,000, the polymer may make undesired influence on the mechanicalproperties of the films. Any homopolymer formed of one type repeatingunit or copolymers having plural repeating units formed can be used. Twoor more types of the polymers described above may be used; and thepolymers may be used along with any other plasticizer, antioxidant,acid-trapping agent, UV absorbing agent, slipping agent or mat agent.

The amount of the compound in the film is preferably from 0.5 to 50% bymass, more preferably for 1 to 30% by mass and much more preferably from1 to 15% by mass with respect to the mass of the polymer material suchas acryl-base polymer. The amount of the compound may be decideddepending on the purpose of addition of the compound.

Mat Agent:

The optical compensation film (for example, acryl-base polymer film) ofthe invention may contain mat agent (occasionally referred to as “fineparticles” hereinunder). The fine particles include fine particles ofinorganic compounds, and fine particles of organic compounds, and anythese are usable herein. The mean primary particle size of the fineparticles to be in the thermoplastic polymer for use in the invention ispreferably from 5 nm to 3 μm from the viewpoint of reducing the haze ofthe film, more preferably from 5 nm to 2.5 μm, even more preferably from10 nm to 2.0 μm. The mean primary particle size of fine particles asreferred to herein is determined as follows: A thermoplastic polymercomposition is observed with a transmission electronic microscope(having a magnification of from 500,000 to 1,000,000 powers), and theprimary particle size of 100 particles is measured, and the data areaveraged to be the mean primary particle size of the fine particles. Theamount of fine particles to be added is preferably from 0.005 to 1.0% bymass relative to the thermoplastic polymer, more preferably from 0.01 to0.8% by mass, even more preferably from 0.02 to 0.4% by mass.

The mean secondary particle size of the fine particles in the obtainedpolymer film is preferably from 0.01 to 5, more preferably from 0.02 to3 μm, even more preferably from 0.02 to 1 μm. The mean secondaryparticle size of fine particles as referred to herein is determined asfollows: A polymer film is observed with a transmission electronicmicroscope (having a magnification of from 100,000 to 1,000,000 powers),and the secondary particle size of 100 particles is measured, and thedata are averaged to be the mean secondary particle size of the fineparticles.

Examples of the inorganic compound include SiO₂, ZnO, TiO₂, SnO₂, Al₂O₃,ZrO₂, In₂O₃, MgO, BaO, MoO₂, V₂O₅, talc, clay, sintered kaolin, sinteredcalcium silicate, hydrated calcium silicate, aluminum silicate,magnesium silicate and calcium phosphate. Preferred are SiO₂, ZnO, TiO₂,SnO₂, Al₂O₃, ZrO₂, In₂O₃, MgO, BaO, MoO₂ and V₂O₅; and more preferredare SiO₂, TiO₂, SnO₂, Al₂O₃ and ZrO₂.

As fine particles of silicon dioxide, SiO₂, for example, commercialproducts of Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50,TT600 (all by Nippon Aerosil) are usable. As fine particles of zirconiumoxide, ZrO₂, for example, commercial products of Aerosil R976 and R811(both by Nippon Aerosil) are usable. And SEAHOSTAR KE-E10, E30, E40,E50, E70, E150, W10, W30, W50, P10, P30, P50, P100, P150 and P250 (byNIPPON SHOKUBAI) are also usable. And Silica micro beads P-400 and 700(by SHOKUBAI KASEI KOGYO) are also usable. And SO-G1, SO-G2, SO-G3,SO-G4, SO-G5, SO-G6, SO-E1, SO-E2, SO-E3, SO-E4, SO-E5, SO-E6, SO-C1,SO-C2, SO-C3, SO-C4, SO-05 and SO-C6 (by Admatechs) are also usable. AndSilica particles 8050, 8070, 8100 and 8150 which are obtained bypowderization of water-dispersion (by MORITEX Corporation) are alsousable.

Organic fine particles such as crosslinked acryl and crosslinkedstyrene; and elasticity organic fine particles described inJP-A-2008-9378 and 2008-74918; are also usable.

Among the inorganic and organic fine particles, in terms of heatstability in the film-forming step, inorganic fine particles arepreferable, and SiO₂ fine particles are more preferable.

A master pellet containing polymer material and fine particles in theamount more than the desired ratio may be prepared previously. Using it,pellets in which fine particles are dispersed well can be prepared, andit is possible to prepare an acryl-base polymer film having a good planecondition and good slipping properties. It may be necessary to prepareanother master pellet not containing fine particles. The master pelletcontaining fine particles preferably also contains a stabilizer. Theamount of fine particles in the master pellet is not limited, andpreferably, the amount of fine particles in the master pellet is from 2to 50 times, more preferably from 2 to 30 times, much more preferablyfrom 3 to 25 times, and even more preferably from 4 to 20 times of theamount of fine particles in the film. Mixing the master pellets may becarried out by using mixer. Any additive(s) such as a stabilizer,plasticizer or other additive may be added to the master pelletcontaining fine particles. In such a case, the amount of the additive(s)in the master pellet is preferably from 2 to 50 times, more preferablyfrom 2 to 30 times, much more preferably from 3 to 25 times, and evenmore preferably from 4 to 20 times of the amount of fine particles inthe film.

Other Additives:

As other additive(s), an IR absorbing agent or retardation controllingagent may be added to the film; and the types of these additives are notlimited. The amount of the other additive(s) is preferably from 0 to1000 ppm, more preferably from 0.1 to 5% by mass, and much morepreferably from 0.2 to 3% by mass.

1.-2 Production Method for Optical Compensation Film:

The optical compensation film of the invention may be produced accordingto a solution casting method or a melt casting method, but is producedpreferably according to a melt casting method. Especially preferably,the acryl-base polymer film of one embodiment of the invention isproduced according to a melt casting method. It is generally known thatan acryl-base polymer is easy to thermally decompose, and a lactone ringunit-containing acryl-base polymer, a maleic anhydride unit-containingacryl-base polymer and a glutaric anhydride unit-containing acryl-basepolymer are easier to thermally decompose than ordinary acryl-basepolymers. On the other hand, the physical properties of a lactone ringunit-containing acryl-base polymer, a maleic anhydride unit-containingacryl-base polymer and a glutaric anhydride unit-containing acryl-basepolymer are that they have a higher Tg and have a higher lighttransmittance than ordinary acryl-base polymers, and therefore, they arefavorable as materials for liquid-crystal display devices.

In addition, the properties of the acryl-base polymer film formed of theacryl-base polymer are that the film has a small elongation at break andthat, when the film surface is rubbed, the acrylic molecules are readilycut and the rubbed part of the film tends to be a striking scratch; andtherefore, when the acryl-base polymer film is formed according to aconventional method, it may readily have rubbed scratched.

When the acryl-base polymer that is easy to thermally decompose is used,especially when the lactone ring unit-containing acryl-base polymer, themaleic anhydride unit-containing acryl-base polymer and the glutaricanhydride unit-containing acryl-base polymer that are easier tothermally decompose are used, the acryl-base polymer film is preferablyproduced according to the production method to be mentioned below.According to the production method to be mentioned below, the acryl-basepolymer film satisfying the above-mentioned optical characteristics canbe produced stably. In addition, according to the production method tobe mentioned below, the generation of impurities derived from thermaldecomposition can be significantly inhibited and acryl-base polymerfilms free from film surface defects can be produced. Specifically, whena polymer that is easy to thermally decompose is used as the material infilm formation, the melting temperature of the polymer could not behigh, and therefore the viscosity of the polymer melt must be kept highduring film formation. When such a high-viscosity melt is used in filmformation, then it may be stretched by a large force at the die outletport, and a great shear may be given to the film between a touch rolland a chill roll. As a result, even when a high-viscosity acryl-basepolymer melt is used in the acryl-base polymer film production method tobe mentioned below, an acryl-base polymer film satisfying the necessaryoptical characteristics can be produced stably. In addition, accordingto the production method to be mentioned below, a shear may be given tothe film surface and the acrylic molecules of the film are therebystretched to increase the entanglement between the molecules and toincrease the elongation at break of the film; and, as a result, theobtained acryl-base polymer film may have few scratches.

Needless-to-say, any other thermoplastic polymer film comprising, as themain ingredient thereof, any other thermoplastic polymer than acryl-basepolymer (e.g., cycloolefin-base polymer film) can also be produced forthe optical compensation film of the invention, according to theproduction method to be mentioned below.

Concretely, the film of the invention is produced preferably accordingto a method comprising a step of preparing a molten polymer (melt), astep of extruding the melt through a die, and a step of solidifying themelt extruded through the die, on a casting roll and forming it into afilm. In the step of solidifying the melt extruded through the die, on acasting roll and forming it into a film, preferably, a touch roll isused to press the melt against the casting roll, whereupon a peripheralspeed difference in the revolution therebetween is given to the touchroll and the casting roll and a temperature difference of from 0.1° C.to 15° C. therebetween is also given to the two. In this step, anacryl-base polymer film of which the tilt angle of the main axissatisfies β≠0 and |β|≦45 can be produced stably.

The production method is described in detail hereinunder.

1.-2-1 Melting Step:

First, a polymer melt is melt in a melting step. Concretely, a polymermaterial and an additive are mixed and pelletized, then put into akneading extruder, melt therein to give a molten polymer (hereinafterthis may be referred to as a melt). The pellets are produced as follows:The polymer and the additive are dried and mixed to give a mixturehaving a water content of at most 0.1%, then the mixture is introducedinto the extruder, melted therein at 150° C. to 300° C., and the mixturemelt is extruded out as noodles, which are then cut and solidified inair or in water to give pellets. After melted in the extruder, themixture melt may be directly cut while extruded into water through anozzle thereby giving pellets, according to an underwater cuttingmethod.

The extruder includes a single-screw extruder, a non-engagingcounter-rotating double-screw extruder, an engaging counter-rotatingdouble-screw extruder, an engaging uni-rotating double-screw extruder,etc. Preferably, the number of revolutions of the extruder is from 10rpm to 1000 rpm, more preferably from 20 rpm to 700 rpm. The extruderretention time is preferably from 10 seconds to 10 minutes, morepreferably from 20 seconds to 5 minutes.

Not specifically defined, the size of the pellets may be generally from10 mm³ to 1000 mm³ or so, preferably from 30 mm³ to 500 mm³ or so.

Preferably, prior to feeding the melt of thermoplastic polymercomposition, the water content of the pellets is reduced. Preferably,the drying temperature is from 40 to 200° C., more preferably from 60 to150° C. Accordingly, the water content is preferably reduced to at most1.0% by mass, more preferably at most 0.1% by mass. The drying may beattained in air, or in nitrogen, or in vacuum.

Next, the dried pellets are fed into the cylinder via the feeding portof the extruder, and kneaded and melted therein. Preferably, the insideof the cylinder comprises, for example, a feeing zone, a pressing zone,and a metering zone in that order from the side of the feeing port. Thescrew compression ratio of the extruder is preferably from 1.5 to 4.5;the ratio of the cylinder length to the cylinder inner diameter (L/D) ispreferably from 20 to 70; and the cylinder inner diameter is preferablyfrom 30 mm to 150 mm. Further, for preventing the polymer melt frombeing oxidized with the remaining oxygen in the extruder, preferably,the extruder is purged with an inert gas (e.g., nitrogen), or isdegassed in vacuum via a vent.

Preferably, a filter unit with a breaker plate-type filter or aleaf-type disc filter is fitted to the system for removing impuritiesfrom the thermoplastic polymer composition by filtration therethrough.The filtration may be one-stage or multi-stage filtration. Preferably,the filtration accuracy is from 2 μm to 15 μm, more preferably from 3 μmto 10 μm. Stainless steel is preferred for the filter material. Thefilter constitution includes knitted wire nets, and sintered metal fiberor metal powder articles (sintered filters); and preferred are sinteredfilters.

The filtration is preferably carried out after the end of the mixingstep in the extrusion before the extrusion step of extruding the meltfrom die. It is not preferable that the melt extruded from die issubjected to a filtration since such a treatment likely causescontamination.

For increasing the thickness accuracy by reducing the melt dischargefluctuation, preferably, a gear pump is disposed between the extruderand the thermoplastic polymer composition feeding means (e.g., die).Accordingly, the polymer pressure fluctuation inside the thermoplasticpolymer composition feeding means (e.g., die) may be reduced to ±1%. Forenhancing the constant feeding capability of the gear pump, there may beemployed a method of changing the number of screw revolutions to therebyconstantly control the pressure before the gear pump.

The difference in pressure between the entrance and exit of a gear pumpis preferably from 1 MPa to 15 MPa, more preferably from 1.5 MPa to 13MPa, and much more preferably from 2 MPa to 12 MPa. In the description,the term “the difference in pressure between the entrance and exit of agear pump” means the absolute value of the difference between themeasured pressures by the pressure indicators disposed in front of andin the back of a gear pump.

Adjusting the difference in pressure between the entrance and exit of agear pump to the range from 1.5 MPa to 13 MPa may make it easy to carryout wide film-forming, which gives films having a desired width.Previously, according to the wide film-forming process, the amount ofextrusion increased, and therefore, the number of rotations of the screwalso increased, which resulted in the unevenness in the thickness of theobtained film due to the unevenness of the number of rotations.Disposing a gear pump may contribute to reducing such unevenness in thethickness. On the other hand, an acryl-base polymer film is easilydecomposed by heat, and the yellowish discoloration may occur in thefilm due to the heat decomposition. Such a yellowish discoloration mayincrease the wavelength dispersion characteristics, and, sometimes, theymay become to fall without the desired range. This may cause thesignificant color shift in the black state. Furthermore, thecontamination may be promoted due to the heat decomposition, which isundesirable. By adjusting the difference in pressure between theentrance and exit of a gear pump to the above described range, it ispossible to prevent retention from occurring and to solve theseproblems.

The pressure at the entrance of the gear pump may be higher or lowerthan that at the exit. The difference in pressure may be achieved bycontrolling the extruded amount from the extruder and the number ofrotations of the gear pump. The difference in pressure may be achievedalso by varying pressure loss due to the difference between thediameters of the pipes of the entrance and exit of the gear pump. Whensuch a difference in pressure is present, the retention of the melt isprevented.

It is to be noted that, usually, the film-forming is carried out withalmost no difference in pressure between in front of and in the back ofa gear pump.

For preventing the retention of the melt from occurring, a static mixeris preferably disposed on the pipe between the extruder and the die.

The static mixer may be disposed any place on the pipe between theextruder and the die, and is preferably disposed between the filtrationmechanism and the die and more preferably disposed in front of andadjacent to the entrance of the die.

The number of the elements of the static mixer is preferably from 4 to50, more preferably from 5 to 40 and much more preferably from 6 to 30.Because of slow flow-speed and the long retention time of the melt,there may more often cause any contaminant due to the heat decompositionin any portion being close to the wall of the pipe, compared with in thecenter portion of the pipe. By using a static mixer, the agitation ofthe melt in the pipe may be promoted and therefore the retention of themelt may be prevented.

The static mixer is preferably created by disposing the above mentionednumbers of rectangular plates twisted with an twisting angle of from 30°to 360° (preferably from 60° to 240°, more preferably from 80° to 200°)along the pipes. By allowing the melt to go through the static mixerhaving such a structure, the melt may be rotated and the agitation ofthe melt in the pipe may be promoted. The length of a static mixer isnot limited, and the length is preferably from 0.5 to 10 times, morepreferably from 0.8 to 6 times and much more preferably from 1.0 to 3times of the diameter of the pipe.

The material of the static mixer is not limited, and is preferablystainless steel. Preferably, the coat of hard chrome or tungsten carbideis applied.

1.-2-2 Step of Extruding the Polymermelt Through Die:

In the extruder having the constitution as above, the polymercomposition is melted, and if desired, the polymer melt is led to passthrough a filter and a gear pump, and thereafter it is continuouslytransferred to a die. The die may be in any type of a T-die, a fishtaildie, or a hanger coat die.

Preferably, the die clearance is controllable in a range of from 5 to 50mm. An automatic thickness control die is also effective, by which thethickness and the thickness deviation of the downstream film arecomputed and the data are fed back for die clearance control.

Apart from the single-layer film forming apparatus, a multilayer filmforming apparatus is also usable herein.

The residence time taken by the polymer composition to run into theextruder via the feeding port and then go out of it via the die ispreferably from 3 minutes to 40 minutes, more preferably from 4 minutesto 30 minutes.

1.-2-3 Step of Solidifying the Melt Extruded Through Die on Casting Rollfor Film Formation Thereon:

Next the polymer melt sheetwise extruded through the die is cooled andsolidified on a casting roll (this may be referred to as a chill roll)to give a film thereon.

In this stage, preferably, the zone between the die and the casting rollis shielded and protected from wind.

When the melt is brought into contact with the casting roll, preferably,the contact between the casting roll and the melt is ensured accordingto an electrostatic method, an air knife method, an air chamber method,a vacuum nozzle method, a touch roll method or the like. Above all,preferred is a touch roll method as in the above. The contact enhancingmethod may be applied to the entire surface of the film melt or may beto a part thereof.

Method Employing Only Casting Roll:

The melt, extruded from the die, is cooled on the casting roll at atemperature of from 80 to 200 degrees Celsius, more preferably from 90to 190 degrees Celsius and much more preferably from 100 to 180 degreesCelsius to be solidified. According to this treatment, the shrinkage inthe side having a lower temperature occurs more than that occurring inanother side having a higher temperature. Therefore, the difference instress (shear stress) between the both sides of the film occurs due tothe difference in the degree of shrinkage between the both sides of thefilm. According to the step, the optical properties satisfying thecondition of that the tilt angle β of the main axis is not equal tozero, β≠0, (preferably, |β|≦45). And such a stress may prompt thealignment of molecules in plane and along the thickness direction, andtherefore, Re and Rth may be developed slightly.

For achieving the difference in the temperature between both sides ofthe film, the alleger extrusion amount of the melt is more preferable.For preparing the acryl-base polymer film, which is an example of theinvention, the extrusion amount of the melt is preferably from 100kg/hour to 500 kg/hour, more preferably from 120 kg/hour to 400 kg/hour,and much more preferably from 140 kg/hour to 300 kg/hour. By adjustingthe extrusion amount to the above mentioned range, the melt, extrudedfrom the die, can reach the casting roll before the temperature of themelt is lowered. After that, the side of the film disposed on thecasting roll is cooled drastically; and, on the other hand, another sideof the film is cooled moderately, which results in the difference in thetemperature between the both sides of the film.

In such an extrusion with a high rotative speed, the shear stressbetween the screw and the barrel may increase, and as a result, thedecomposition of the polymer material due to molecular breaks may bepromoted. As a result, the polymer changes yellowish; the spectralabsorption may be varied; and therefore, the wavelength dispersioncharacteristics of Re and Rth may be adjusted to the preferable range.Regarding the melt before being subjected to this treatment, thewavelength dispersion characteristics of Re and Rth may be zero.

It may be necessary to increase the number of rotations of the screw,and as a result, heat due to shearing force may be developed. Acryl-basepolymers are easily decomposed by heat; and as a result, yellowishdiscoloring is too much, which is undesirable. The contamination due tothe thermal decomposition is increase, which is also undesirable. Forsolving such a problem, in the film-forming step, preferably, thetemperature of the screw at the entrance is higher by a temperature offrom 3 to 50 degrees Celsius, more preferably from 5 to 45 degreesCelsius, and much more preferably from 8 to 40 degrees Celsius, that thetemperature thereof at the exit. In the portion close to the entrance ofthe screw, the pellets are rubbed each other strongly since they are notmelt yet, which causes the friction heat easily. Therefore, it ispreferable to lower the temperature of this portion. On the other hand,in the portion close to the exit of the screw, the pellets are meltfully, which causes the friction heat hardly. Therefore, it ispreferable to increase the temperature of this portion, or that it, thetemperature of the melt, for achieving the difference in the temperaturebetween the both sides of the film.

Furthermore, by increasing the temperature of the exit of the screw, thedecomposition of the polymer material may be promoted, and as a result,the polymer film may change yellowish slightly. Therefore, thewavelength dispersion characteristic of Re and Rth may be adjusted tothe desired range.

It is to be noted that, according to the previous process. the step iscarried out with a constant temperature of the screw, as described inJP-A-2007-297615, Examples 1.

The temperature of the exit of the screw is preferably from 210 to 280degrees Celsius and more preferably from 220 to 270 degrees Celsius.

Method Employing Touch Roll:

In the description, the term “chilled roll” means a casting roll whichcontacting the melt, extruded from die, firstly; and the term “touchroll” means a roll disposed facing with the chilled roll. According tothe method, the melt, extruded from the die, is cooled between the touchroll and the chilled roll to be solidified. It is to be noted that theterm “casting roll” hereinunder indicates both of the chilled roll andany casting rolls following the chilled roll

The method comprises the step of extruding the melt from the die and thestep of allowing the melt to pass between the chilled roll and the touchroll to form a film, wherein the peripheral speeds of the rolls aredifferent from each other. According to the invention, the peripheralspeed ratio of the chilled roll and the touch roll is defined as thefollowing formulae. In one preferable example of the method, theperipheral speed ratio is adjusted to the range of from 0.60 to 0.99,and as a result. shear stress is applied to the melt. The peripheralspeed ratio is preferably from 0.60 to 0.99, and more preferably from0.75 to 0.98.Peripheral speed ratio=peripheral speed of the chilled roll/peripheralspeed of the touch roll  (I)

When the melt is cooled between the casting roll and touch roll, thetemperatures of the rolls are preferably set to fall between (Tg−30° C.)and (Tg+10° C.) where Tg indicates the glass transition temperature ofthe polymer, more preferably between (Tg−20° C.) and (Tg+7° C.), morepreferably between (Tg−10° C.) and (Tg+3° C.). For example, in theembodiments using the acryl-base polymer as a material, the temperaturesare preferably from 60 to 160 degrees Celsius, more preferably from 70to 150 degrees Celsius and much more preferably from 80 to 140 degreesCelsius. However, the temperatures are not limited to the ranges.

The difference in the temperature between the touch roll and the castingroll is preferably from 0.1 to 15 degrees Celsius, more preferably from0.3 to 12 degrees Celsius, and much more preferably from 0.5 to 10degrees Celsius. By adjusting the difference in the temperature betweenthe rolls to the above mentioned range, it is possible to adjust β tothe desired range easily, which is preferable.

The temperature of the touch roll may be higher or lower than that ofthe casting roll; and preferably, the temperature of the touch roll islower than that of the casting roll. After passing through between thetouch roll and the casing roll, the melt is transported on the castingroll. When the temperature of the casting roll is higher, the melt canbe transported more stably on the casting roll having higher temperaturedue to adjustability.

Controlling the temperature of the roll(s) can be performed by flowingany liquid or gas whose temperature is controlled inside of the roll(s).The means for controlling the temperature is preferably disposed inside.Examples of the means for controlling the temperature are as follows. Inthe one embodiment, the touch roll is disposed on a metal shaft, and theheat carrier (fluid) is allowed to pass between them. Or in anotherembodiment, the elastic body is disposed between the external cylinderand the metal shaft, and the external cylinder is filled with the heatcarrier (fluid). In these embodiments, by controlling the temperature ofthe heat carrier, it is possible to control the temperature of the touchroll.

According to the process of preparing the film, the landing point of themelt preferably falls within the range of 10 mm±the center of theclearance between the touch roll and the casting roll, more preferably 5mm±the center, and much more preferably 3 mm±the center.

The term of “the landing point of the melt” indicates the point wherethe melt touches the touch roll or the chilled roll first. And the term“the center of the clearance between the touch roll and the castingroll” indicates the center of the clearance, which is narrowest, betweenthe surfaces of the touch roll and the casting roll.

Usually, the landing point of the melt is the center of the clearance.However, according to the invention, the landing point may depart fromthe center slightly. The landing point of the melt may be on the touchroll or the chilled roll.

The term “the touch pressure” indicates the value which is obtained bydividing the force for pressing touch roll by the contacting area of thefilm and the touch roll.

The touch pressure is preferably from 0.1 MPa to 10 MPa, more preferablyfrom 0.3 MPa to 7 MPa, and much more preferably from 0.5 MPa to 3 MPa.

By adjusting the difference in the temperature between the touch rolland the casting roll and the touch pressure to the above mentionedranges, it is possible to prepare the films having β, Re and Rthsuitable for IPS- or FFS-mode liquid crystal displaying devices.

For achieving such a weak touch pressure, the touch roll havingelasticity is more preferable than that having high rigidity. A touchroll having an external cylinder with a thinner thickness than usual ispreferable. The thickness Z of the external cylinder is preferably from0.05 mm to 7.0 mm, more preferably from 0.2 mm to 5.0 mm and much morepreferably from 0.3 mm to 3.5 mm.

Preferably, the surface of the touch or casting roll has an arithmeticmean height Ra of at most 100 nm, more preferably at most 50 nm, evenmore preferably at most 25 nm. By using the rolls having an arithmeticmean height Ra falling within the abovementioned range, it is possibleto prepare the films having appropriate concavities and convexities.

The touch roll and the casting roll is preferably made of a metal andmore preferably made of stainless. The touch roll and casting rollhaving the metal coat thereon are also preferable. By using the touchroll and the casting roll having the surface made of a metal, it ispossible to adjust Ra of the tolls to the range of not greater than 100nm easily. On the other hand, any rubber roll or any metal roll beingsubjected to a lining application with rubber may have large concavitiesand convexities, and as a result, it is not possible to easily preparethe films having appropriate concavities and convexities.

The touch rolls described in JP-A-11-314263, 2002-36332 and 11-235747and WO97/28950, JP-A-2004-216717 and 2003-145609 may be used in theinvention.

Using plural casting rolls and cooling the melt by them are preferable.In this embodiment, the touch roll may be disposed so as to touch afirst casting roll, which is closest to the die among them, that is, thechilled roll. Usually, 2-6 rolls are used; however the number of therolls is not limited. The diameter of the roll is preferably from 100 mmto 1500 mm, and more preferably from 150 mm to 1000 mm. The clearancebetween the rolls is preferably from 0.3 mm to 300 mm, more preferablyfrom 1 mm to 100 mm, and much more preferably from 3 mm to 30 mm.

In one embodiment, the melt extruded from the die is solidified on thethree or more casting rolls. According to the embodiment, thetemperature of the lower casting roll is lower by a temperature of from1 to 15 degrees Celsius, more preferably from 1 to 10 degrees Celsiusand much more preferably from 2 to 8 degrees Celsius, than thetemperature of the upper casting roll.

By controlling the temperatures of the multiple casting rolls, it ispossible to prompt the improvement of the packing density via thecooling step. As a result, it is possible to easily adjust Ra of thefilm to the desired range. Furthermore, it is possible to make thephysical property of the both sides of a film regularity. Furthermore,it is possible to cancel the distortion in a film. By using such a filmin liquid crystal display devices, it may be possible to reduce thedistortion of the images.

In the method employing the touch roll, the extrusion amount of the meltis preferably from 100 kg/hour to 500 kg/hour. The more preferableranges are same as those in the method not employing the touch roll. Byadjusting the extrusion amount to the above mentioned range, theextrusion speed (line speed) of the melt onto the roll may be elevated,and therefore, the effect of the shrinkage stress may be more developedbetween the both sides of the film. Or in other words, it is possible toapply the deformation to the film for a shorter time, and to prevent β,Re and Rth of the film from relaxing or reducing.

For achieving the extrusion amount, it is helpful to set the temperatureof the exit of the screw higher than that of the entrance. Thewavelength dispersion characteristic of Re and Rth can be adjusted tothe desired range by the effect of theses factors such as the extrusionamount and the temperature of the screw.

1.-2-4 Film Width:

In this description, the film width means the melt width between the dieand the casting roll in the step of extruding the melt through a die;and the melt width is substantially equal to the width of the solidifiedfilm before the trimming step to be mentioned below. The mean value ofthe film width is determined as follows: The width of a film having alength of 10 m, just after formed but before trimmed, is continuouslymeasured and the data are averaged to give the mean value of the filmwidth. The fluctuation of the film width is as follows: The width of afilm having a length of 10 m, just after formed but before trimmed, iscontinuously measured, and the difference between the maximum value andthe minimum value is divided the by the mean film width and is expressedas a percentage.

In the film production method in the invention, the film widthfluctuation is preferably from 1% to 15%, more preferably from 2% to14%, even more preferably from 3% to 12%.

The film width fluctuation can be controlled in film formation to give afilm having a mean width of from 1 m to 3 m, more preferably from 1.4 mto 2.6 m, even more preferably from 1.6 m to 2.4 m.

1.-2-5 Trimming:

Preferably, the formed film is trimmed on both sides thereof. The parttrimmed away from the film may be recycled as a film-forming material.

1.-2-6 Knurling:

Also preferably, the film is knurled on one side or both sides thereof.The height of the knurl to be formed by the knurling treatment ispreferably from 1 μm to 50 μm, more preferably from 3 μm to 20 μm. Inthe knurling treatment, a protrusion may be formed on one surface orboth surfaces. The width of the knurl is preferably from 1 mm to 50 mm,more preferably from 3 mm to 30 mm. The knurling treatment may becarried out at room temperature to 300° C.

1.-2-7 Winding:

After this, the film is peeled away from the casting roll and, afterhaving passed through nip rolls, this is wound up. The winding speed ispreferably from 10 m/min to 100 m/min, more preferably from 15 m/min to80 m/min, even more preferably from 20 m/min to 70 m/min.

Preferably, the winding tension is from 2 kg/m-width to 50 kg/m-width,more preferably from 5 kg/m-width to 30 kg/m-width.

Also preferably, a laminate film may be stuck to one or both surfaces ofthe film. The thickness of the laminate film is preferably from 5 μm to100 μm, more preferably from 10 μm to 50 μm. Not specifically defined,the material may be any of polyethylene, polyester, polypropylene, etc.

1.-2-8 Stretching:

The thermoplastic film formed by melt casting is preferably stretched inthe machine direction and/or in the transverse direction, optionally ascombined with relaxation shrinkage treatment. The film traveling speed(speed before stretching) in the machine-direction stretching and thetransverse-direction stretching treatment is preferably from 10 m/min to50 m/min, more preferably from 12 m/min to 40 m/min, even morepreferably from 15 m/min to 35 m/min.

Machine-Direction Stretching:

The machine-direction stretching may be attained as follows: Two pairsof nip rolls are disposed, and the film to be stretched is led to passthrough them under heat, whereupon the peripheral speed of the nip rollson the outlet port side is made higher than the peripheral speed of thenip rolls on the inlet port side. In this stage, the length (L) betweenthe nip rolls and the width (W) of the unstretched film may be varied,thereby varying the expressibility of the thickness-directionretardation of the stretched film. When UW is from 2 or more to 50 (inlong spun stretching), Rth of the stretched film may be small; and whenUW is from 0.01 to 0.3 (in short spun stretching), Rth thereof may belarge. In producing the optical compensation film of the invention,employable is any method of long spun stretching, short spun stretchingor middle spun stretching between the two (in middle spun stretching,L/W is from more than 0.3 to 2). Preferred is long spun stretching orshort spun stretching in which the alignment angle could be small. Formaking the stretched film have a further higher Rth, preferred is shortspun stretching; and for making the stretched film have a lower Rth,preferred is long spun stretching. In that manner, more preferably, thestretching mode is suitably selected depending on the intendedretardation of the stretched film.

The stretching temperature in the machine-direction stretching ispreferably from (Tg−10) to (Tg+50) degrees Celsius, more preferably from(Tg−5) to (Tg+40) degrees Celsius, and much more preferably from (Tg) to(Tg+30) degrees Celsius. The stretching ratio is preferably from 2% to200%, more preferably from 4% to 150%, and much more preferably from 6%to 100%. In the description, the stretching ratio is defined as follows.Stretching ratio (%)=100×{(length of a stretched film)−(length of anunstretched film)}/(length of an unstretched film)Transverse-Direction Stretching:

The unstretched film may be stretched in the transverse direction, usinga tenter. Specifically, both sides of the film in the y-axis directionare held with clips, and the film is expanded in the transversedirection. In this stage, the stretching temperature may be controlledby introducing air at a predetermined temperature into the tenter. Thestretching temperature in the transverse-direction stretching ispreferably from Tg−10 to Tg+60 degrees Celsius, more preferably fromTg−5 to Tg+45 degrees Celsius, and much more preferably from Tg to Tg+30degrees Celsius. The stretching ratio is preferably from 10% to 250%,more preferably from 20% to 200%, and much more preferably from 30% to150%.

1.-2-9 Heat Treatment:

The film may be preheated before the stretching or may be post-heatedafter the stretching, whereby the fluctuation of the alignment angleowing to bowing of the stretched film may be reduced. One or both of thepreheating and post-heating may be attained; but preferably both of thetwo are attained. Preferably, the preheating treatment and post-heatingtreatment are attained while the film is held with clips, or that is,the treatment is preferably attained in succession to stretching. Inthermal fixation of the film, preferably, the tenter width is keptalmost constant. The wording “almost constant” as referred to herein ismeant to indicate a range of from 0% of the tenter width afterstretching (the same width as the tenter width after stretching) to −10%thereof (the width is reduced to be smaller by 10% than the tenter widthafter stretching=width reduction). Width expansion to be larger than thestretching width is unfavorable since the processed film may haveresidual strain remaining therein.

The postheating is preferable at a temperature lower by from 1 to 50°C., more preferably by from 2 to 40° C., and much more preferably byfrom 3 to 30° C., than the stretching temperature. The temperature inthe postheating is preferably equal to or higher than the stretchingtemperature and equal to or lower than Tg. The postheating time ispreferably from one second to ten minutes, more preferably from fiveseconds to four minutes and from ten seconds to two minutes.

The preheating is preferably at the stretching temperature±50° C., morepreferably at the stretching temperature±35° C., even more preferably atthe stretching temperature±20° C. In case where the film after thepost-heating treatment is bowed convexly in the machine direction, thestretching temperature is preferably lowered more; but when it is bowedconcavely in the machine direction, then the stretching temperature ispreferably raised higher. The preheating time is preferably from 1second to 10 minutes, more preferably from 5 seconds to 4 minutes, evenmore preferably from 10 seconds to 2 minutes. In the preheating,preferably, the tenter width is kept almost constant. The wording“almost constant” as referred to herein means±10% of the width of theunstretched film.

To that effect, preferably, thermal fixation temperature<stretchingtemperature<preheating temperature.

As a result of the stretching of that mode, the fluctuation of Re andRth in the y-axis direction and in the x-axis direction, and also thedeviation of the alignment angle from MD (x-axis direction) or TD(y-axis direction) can be reduced.

1.-2-10 Relaxation Treatment:

Preferably, the film is processed for relaxation after the MD and/or TDstretching. For the relaxation, preferably, the film is heated at Tg±40°C., more preferably at Tg±30° C., even more preferably at Tg±20° C.,under low tension (preferably from 0.1 to 10 kg/m, more preferably from0.2 to 5 kg/m, even more preferably from 0.3 to 3 kg/m), for preferablyfrom 0.1 minutes to 30 minutes, more preferably from 0.3 minutes to 15minutes, even more preferably from 0.5 minutes to 8 minutes. Through thetreatment for relaxation, the residual strain remaining inside the filmcan be removed not changing the birefringence (retardation) of the filmexpressed by stretching.

1.-2-11 Processing of Film:

Preferably, the optical compensation film of the invention may becombined with a functional layer described in detail in Hatsumei KyokaiBulletin (No. 2001-1745, published on Mar. 15, 2001 by the HatsumeiKyokai), pp. 32-45. Especially preferably, a polarizing layer is addedto the film to produce a polarizing plate; an optically-anisotropiclayer is added thereto; or an antireflection layer is added thereto toproduce an antireflection film.

Surface Treatment:

The optical compensation film of the invention may be processed forsurface treatment for enhancing the adhesiveness thereto to any othermembers (e.g., polarizing element). The surface treatment includes, forexample, corona discharging, glow discharging, UV irradiation, flametreatment, etc.

Processing into Polarizing plate:

A polarizing plate usable in the liquid-crystal display device of theinvention can be produced by laminating at least a polarizing element(hereinafter this may be referred to as a polarizing film) on theoptical compensation film of the invention. The polarizing plate usablein the liquid-crystal display device of the invention is describedbelow.

The polarizing plate is not specifically defined in point of itsconstitution, and it may be any one comprising the optical compensationfilm of the invention and a polarizing element. For example, in thepolarizing plate comprising a polarizing element and twopolarizer-protective films (transparent polymer films) for protectingboth surfaces of the element, the optical compensation film of theinvention may be at least one of the polarizer-protective films. For thepurpose of enhancing the adhesiveness between a polarizing element of apolyvinyl alcohol film or the like and the optical compensation film ofthe invention, a layer of a material having good adhesiveness to thematerial of the polarizing element may be formed on the surface of theoptical compensation film of the invention, and the surface of thepolarizing element may be stuck to the surface of that layer. Forexample, a cellulose acylate has a relatively good adhesiveness to apolyvinyl alcohol film. Preferably, therefore, a coating liquid of acellulose acylate is applied to the surface of the optical compensationfilm of the invention to thereby form a cellulose acylate layer thereon,and the surface of that layer is stuck to the surface of a polarizingelement optionally via an adhesive given therebetween. The polarizingplate may have, on at least one surface thereof, an adhesive layer viawhich the polarizing plate is stuck to any other member. In thepolarizing plate, when the surface of the optical compensation film ofthe invention has a roughened structure, then the polarizing plate mayhave an antiglare function. In the polarizing plate, also preferablyused is an antireflection film produced by laminating an antireflectionlayer (low-refractivity layer) on the surface of the opticalcompensation film of the invention, or a lamination film produced bylaminating an optically-anisotropic layer on the surface of the opticalcompensation film of the invention.

In general, a liquid-crystal display device comprises a liquid-crystalcell disposed between two polarizing plates, therefore having fourpolarizer-protective films. The optical compensation film of theinvention may be any of those four polarizer-protective films, but isespecially advantageously used as the protective film to be disposedbetween the liquid-crystal cell and the polarizing plate in theliquid-crystal display device.

More preferably, the polarizing plate has a constitution of a protectivefilm (e.g., cellulose acylate film), a polarizing element and theoptical compensation film of the invention formed of the above-mentionedacryl-base polymer film or the like, as laminated in that order. Alsopreferably, the polarizing plate may have a constitution of a protectivefilm of a cellulose acylate or the like, a polarizing element, theoptical compensation film of the invention formed of the above-mentionedacryl-base polymer film or the like, and an adhesive layer, as laminatedin that order.

2. IPS-mode and FFS-mode Liquid-Crystal Display Device:

The invention also relates to an IPS-mode or FFS-mode liquid-crystaldisplay device comprising the optical compensation film of theinvention. The optical compensation film of the invention may beincorporated in the liquid-crystal display device as an independentmember of the device or as a part of the constitutive member thereof,for example, as a protective film for the polarizing plate in thedevice, or the like.

2.-1 IPS-Mode Liquid-Crystal Display Device:

An IPS mode is a mode of a liquid-crystal display device in which theliquid-crystal material is aligned nearly in parallel to each other atthe time of black level of display. In this, therefore, theliquid-crystal molecules are aligned in parallel to the surface of thesubstrate in no voltage application thereto, at the time of black levelof display. The IPS-mode liquid-crystal display device of the inventionhas the advantage of little light leakage in oblique directions at thetime of black level of display.

FIG. 1 is a schematic cross-sectional view of one example of theIPS-mode liquid-crystal display device of the invention. In FIG. 1, therelative relationship in the thickness between the constitutive layersdoes not reflect the relative relationship in the thickness in an actualliquid-crystal display device. The same shall apply to FIG. 2 and FIG.3.

The liquid-crystal display device of FIG. 1 comprises an IPS-modeliquid-crystal cell LC, a polarizing plate PL1 on the panel side, and apolarizing plate PL2 on the backlight side. The polarizing plates PL1and PL2 each comprise a polarizing element 10, an optical compensationfilm 12 of the invention satisfying the above-mentioned predeterminedcharacteristics, and a protective film 14 of a cellulose acetate film orthe like, in which the optical compensation film 12 of the invention isdisposed between the polarizing element 10 and the IPS-modeliquid-crystal cell LC. The two polarizing elements 10 are so disposedthat their absorption axes 10 a are perpendicular to each other; and thetwo optical compensation films 12 are so disposed that one of theirin-plane slow axes 12 a is in parallel to the absorption axis 10 a ofthe polarizing element 10 disposed adjacent to the film and that theother thereof is perpendicular thereto. The rubbing axis in rubbingtreatment given to the substrate of the liquid-crystal cell LC isperpendicular to the absorption axis 10 a of the polarizing element 10of the polarizing plate PL1 and is in parallel to the absorption axis 10a of the polarizing element 10 of the polarizing plate PL2.

The product of the birefringence Δn of the liquid-crystal molecules inthe liquid-crystal layer (liquid-crystal material) of the liquid-crystalcell LC and the liquid-crystal cell gap d, (Δn×d) may be from 250 nm to400 nm or so. More preferably, the product is from 270 nm to 390 nm,even more preferably from 280 nm to 380 nm. The product (Δn×d) ispreferably from 250 nm to 400 nm, as capable of increasing the displaycontrast. The cell gas d is preferably from more than 2.8 μm to lessthan 4.5 μm. The liquid-crystal cell gap d can be controlled by the useof polymer beads, glass beads or fibers, resinous pillar spacers, etc.As the liquid-crystal material to form the liquid-crystal layer(liquid-crystal cell), usable is a nematic liquid crystal having apositive dielectric anisotropy Δ∈. Not specifically defined, any andevery nematic liquid crystal having the characteristic can be used asthe liquid-crystal material. Preferably, the dielectric anisotropy Δ∈ ofthe liquid-crystal material for use herein is smaller, as capable ofreducing the driving voltage for the device; and the refractivityanisotropy Δn thereof is also preferably smaller since the thickness(gap) of the liquid-crystal layer could be larger and the time to betaken for injecting the liquid crystal into the cell can be shorted moreand the gap fluctuation can be reduced more.

In the liquid-crystal cell LC, the liquid crystal is alignedhorizontally as running along the rubbing axis in no application ofdriving voltage thereto at the time of black level of display. However,the device has a pretilt angle in some degree, in which, therefore, theliquid crystal is not in a completely horizontal alignment state, andthe alignment state of the liquid crystal is asymmetric relative to theaxis inclined from the normal line direction. The IPS-modeliquid-crystal display device of FIG. 1 has the optical compensationfilm 12 disposed therein, and is therefore free from a problem of lightleakage in oblique directions at the time of black level of display, andin addition, this is also free from the problem of asymmetricity, andcan attain more ideal black display. For example, an embodiment wherethe tilt angle β of the main axis of the optical compensation film 12 isβ≠0 and |β|≦45 is effective for solving the problem of light leakage atthe time of black level of display, for an IPS-mode liquid-crystal cellLC having a pretilt angle of from 0.2 to 10° or so. For realizing theeffect of the optical compensation film of the invention, preferably,the optical compensation film of the invention is so disposed in thedevice that pretilt direction of the liquid-crystal layer is the same asthe tilt direction of the main axis of the optical compensation film oris opposite thereto (in the mirror-symmetric direction).

FIG. 2 is a schematic cross-sectional view of another example of theIPS-mode liquid-crystal display device of the invention. The samereference numeral or sign is given to the same member like in FIG. 1,and its description is omitted herein.

The liquid-crystal display device of FIG. 2 has a polymer film 16between a polarizing plate PL1′ on the panel side and the IPS-modeliquid-crystal cell LC. As the polymer film 16, preferred is acycloolefin-base polymer film comprising a cycloolefin-base polymer asthe main ingredient thereof. The cycloolefin-base polymer film may be acommercial product, and for example, JSR's Arton film is usable. Thepolymer film 16 is so disposed that its in-plane slow axis 16 a is inparallel to the absorption axis 10 a of the polarizing element 10 of thepolarizing plate PL1′. The polarizing plate PL1′ on the panel side has aprotective film 14 of a cellulose acetate film or the like having Re ofaround 3.0 nm or so and having Rth of around 45 nm or so on bothsurfaces of the polarizing element 10.

Having the optical compensation film 12 of the invention that satisfiesthe above-mentioned predetermined characteristics, the liquid-crystaldisplay device of FIG. 2 solves the problem of the asymmetricity inlight leakage occurring in oblique directions at the time of black levelof display, like the liquid-crystal display device of FIG. 1.

FIG. 3 is a schematic cross-sectional view of still another example ofthe IPS-mode liquid-crystal display device of the invention. The samereference numeral or sign is given to the same member like in FIG. 1,and its description is omitted herein.

The liquid-crystal display device of FIG. 3 has a positive C-plate 18between a polarizing plate PL1″ on the panel side and the IPS-modeliquid-crystal cell LC. The positive C-plate may be formed of anymaterial such as a polymer material, a liquid-crystal material, etc. Thepolarizing plate PL1″ on the panel side has an optically-biaxialprotective film 14′ between the polarizing element 10 and the positiveC-plate 18. The protective film 14′ satisfying the characteristic may bea commercial product. The protective film 14′ is so disposed that itsin-plane slow axis 14′a is in parallel to the rubbing axis in rubbingtreatment applied to the substrate of the liquid-crystal cell LC. In anembodiment where the positive C-plate 18 is a non-self-supporting layerformed by coating, transcription or the like, the protective film 14′preferably functions also as the support for the positive C-plate. Inthis description, the positive C-plate is a retardation member having Reof nearly zero and having Rth of from 0 to 300 nm or so.

Having the optical compensation film 12 of the invention that satisfiesthe above-mentioned predetermined characteristics, the liquid-crystaldisplay device of FIG. 3 solves the problem of the asymmetricity inlight leakage occurring in oblique directions at the time of black levelof display, like the liquid-crystal display device of FIG. 1; andfurther, as additionally having the optically-biaxial protective film14′ and the positive C-plate 18, the device is more effective forovercoming the problem of light leakage and can therefore attain furthermore ideal black display.

For the concept of IPS-mode liquid-crystal display devices, for example,herein referred to are the descriptions in JP-A 2003-15160, 2003-75850,2003-295171, 2004-12730, 2004-12731, 2005-106967, 2005-134914,2005-241923, 2005-284304, 2006-189758, 2006-194918, 2006-220680,2007-140353, 2007-178904, 2007-293290, 2007-328350, 2008-3251,2008-39806, 2008-40291, 2008-65196, 2008-76849, 2008-96815.

2.-2 FFS-mode Liquid-Crystal Display Device:

An FFS-mode liquid-crystal cell has a counter electrode and a pixelelectrode. These electrodes are formed of a transparent substance suchas ITO or the like, and are so designed as to have a width narrower thanthe distance between the upper and lower substrates and capable ofdriving all the liquid-crystal molecules disposed above the electrode.Having the constitution, the FFS mode can realize a further higheraperture ratio than in the IPS mode. In addition, since the electrodepart is light-transmissive therein, the FFS mode can realize a furthermore increased light transmittance than the IPS mode. For the concept ofFFS-mode liquid-crystal cell display devices, for example, hereinreferred to are the descriptions in JP-A 2001-100183, 2002-14374,2002-182230, 2003-131248, 2003-233083.

As having the optical compensation film of the invention disposedtherein, or as having the optical compensation film of the inventiondisposed therein as combined with the additional film having theabove-mentioned predetermined optical characteristics, the FFS-modeliquid-crystal display device of the invention can realize ideal blackdisplay, like the above-mentioned IPS-mode liquid-crystal displaydevices of the invention. In the FFS-mode liquid-crystal display device,preferably, the optical compensation film of the invention is disposedbetween the liquid-crystal cell and the polarizing element on the panelside.

EXAMPLES

The characteristic features of the invention are described moreconcretely with reference to the following Examples and ComparativeExamples. In the following Examples, the materials used, their amountand their ratio, the details of the treatment and the treatment processmay be suitably modified or changed not overstepping the sprit and thescope of the invention. Accordingly, the scope of the invention shouldnot be limitatively interpreted by the following Examples.

1. Production of Acryl-Base Polymer Film 1.-1 Preparation of Acryl-BasePolymer

Lactone Ring Unit-Containing Acryl-Base Polymer LA-1:

A lactone ring unit-containing acryl-base polymer LA-1 was prepared.

According to Production Example 1 in [0222] to [0224] in JP-A 2008-9378,an acryl-base polymer LA-1 having a degree of lactonization of 98% andTg=134° C. was produced from 7500 g of methyl methacrylate and 2500 g ofmethyl 2-(hydroxymethyl)acrylate.

Maleic Anhydride Unit-Containing Acryl-Base Polymer MA-1:

Asahi Kasei Chemicals' Delpet 980N was prepared as a maleic anhydrideunit-containing acryl-base polymer MA-1. The acryl-base polymer has Tgof 117° C., and contains 15 mol % of maleic anhydride, 18 mol % ofstyrene and 67 mol % of methyl methacrylate of all the constitutivemonomers.

1.-2 Production Example for Acryl-Base Polymer Film

The prepared acryl-base polymer MA-1 was dried in a vacuum drier at 90°C. to make it have a water content of at most 0.03%, and 0.3% by weightof a stabilizer (Irganox 1010 (by Ciba-Geigy)) was added thereto. Usinga vented double-screw kneading extruder, this was extruded out intowater as strands, in a nitrogen current atmosphere at 230° C., and thecut into pellets having a diameter of 3 mm and a length of 5 mm.

The pellets were dried in a vacuum drier at 90° C. to make them have awater content of at most 0.03%, and then, using a single-screw kneadingextruder, this was kneaded and extruded out at the temperature shown inTable 1. Next, a 300-mesh screen filter was disposed between theextruder and a gear pump. Next, this was led to pass through the gearpump under the condition shown in Table 1, then led to pass through aleaf disc filter having a filtration accuracy of 7 μm, and the melt wasextruded out through a die, and cast under the condition shown inTable 1. “Differential pressure before and after gear pump” in Table 1is a value computed by subtracting the backside pressure from the frontside pressure; and in “deviation of melt landing point from touchroll/casting roll intermediate point”, the positive data mean that themelt landed on the touch roll side, and the negative data means that themelt landed on the casting roll side.

After the above, the melt (polymer melt) was extruded out onto a seriesof three casting rolls. In this, a touch roll was kept in contact withthe most upstream casting roll (chill roll) under the surface pressureshown in Table 1 below. As the touch roll, herein used was one describedin Example 1 in JP-A 11-235747 (as double-press roll; in this, however,the thickness of the thin-wall metal jacket was changed to 2 mm), andthis was used under the touch pressure shown in Table 1 at Tg−15° C. Thetemperature of the series of three casting rolls including the chillroll was so controlled that the casting roll (first roll) kept incontact with the touch roll on the most upstream side could have thetemperature difference (casting roll temperature−touch roll temperature)as in Table 1. The next casting roll (second roll) was kept at thetemperature of the first roll−5° C.; and the following casting roll(third roll) was kept at the temperature of the first roll−10° C.

Next, just before wound up, the film was trimmed on both sides thereof(by 5 cm of the overall width), and then knurled on both sides thereofto a width of 10 mm and a height of 20 μm. The final film width was 1.5m and the film was wound up at a film formation speed of 30 m/min to alength of 3000 m. The thickness of the thus-produced, unstretched filmwas 60 μm. The acryl-base polymer film is an acryl-base polymer film 1of the invention.

Acryl-base polymer films 2 to 4 of the invention were produced in thesame manner as in Example 1, for which, however, the acryl-base polymer,the screw temperature difference, the extrusion rate, the differentialpressure before and after the gear pump, the temperature differencebetween the surface and the back of the melt on the casting roll, theperipheral speed of the casting roll and the touch roll, the temperaturedifference between the casting roll and the touch roll, the melt landingpoint and the touch pressure of the touch roll were changed as in Table1 below.

An acryl-base polymer film C1 of Comparative Example was produced alsoin the same manner as in Example 1, for which, however, the acryl-basepolymer and the condition for film formation were changed as in Table 1below.

The acryl-base polymer films 1 to 4 and the comparative acryl-basepolymer film C1 were analyzed according to the methods mentioned in theabove to determine the tilt angle β[°], and also Re, Rth and thewavelength dispersion characteristics thereof. The results are shown inTable 2 below.

TABLE 1 Acryl-base polymer (2) (3) (4) (5) (6) (7) (8) (9) (10) film (1)(° C.) (Kg/hr) (MPa) (° C.) (m/min) (m/min) (° C.) (mm) (MPa) 1 MA-1 25300 10 — 5.1 5.0 15 −0.6 1.5 2 MA-2 25 300 10 — 5.2 5.0 15 −0.6 5 3 MA-225 300 10 — 5.8 5.0 15 −0.6 15 4 MA-1 25 300 10 — 5.05 5.0 15 −0.6 1.0C1 LA-1 2 80 5 70 — 10.0 *1 (1) the material (2) the screw temperaturedifference (the temperature of the exit - the temperature of theentrance) (3) the extrusion amount (4) the difference in the pressurebefore and after the gear pump (the pressure in front of the gear pump -the pressure in the back of the gear pump) (5) the temperaturedifference between the both sides of the melt on the casting roll (6)the peripheral speed of the touch roll (7) the peripheral speed of thecasting roll (8) the temperature difference between the casting roll andthe touch roll (9) the disagreement of the melt landing point from thecenter of the clearance between the touch roll and the casting roll (10)the touch pressure of the touch roll *1: Any touch roll was not used.

TABLE 2 Wavelength Wavelength Acryl-base Re Rth dispersion dispersion ofβ polymer film (nm) (nm) of Re *1 Rth *2 (°) 1 9 −29 0.2 1.6 15 2 3 −60.1 1.2 30 3 5 −10 0.2 1.1 45 4 5 −7 0.2 1.4 10 C1 0 0 0.2 1.2 0 *1:|Re(630)-Re(450)| *2: |Rth(630)-Rth(450)|

2. Production of COC Film

TOPAS #6013 pellets (Tg=136° C.) were used. These were dried at 110° C.for 2 hours or more, and then extruded using a single-screw kneadingextruder. In this, a screen filter, a gear pump and a leaf disc filterwere disposed in that order between the extruder and the die, and thesewere connected to each other via a melt pipe line. The melt was extrudedout at an extrusion temperature of 260° C. through the die having awidth of 1900 mm and a lip gap of 1 mm.

Next, the polymer melt was extruded out onto the center part of a chillroll and a touch roll. In this, the chill roll was a HCr-plated metalroll having a width of 2000 mm and a diameter of 400 mm; and the touchroll was one described in a first embodiment of JP-A 11-235747 having awidth of 1700 mm and a diameter of 350 mm (as double-press roll; inthis, however, the thickness of the thin-wall metal jacket was changedto 2 mm). The touch pressure was measured by sandwiching a prescale (byFUJIFILM) between the two rolls running at the same peripheral speed (5m/min) with no melt therebetween, and the touch roll pressure wascontrolled as in the Table below.

Using these rolls, the touch roll peripheral speed, the chill rollperipheral speed, and the peripheral speed ratio were controlled as inthe Table below. The touch roll and the chill roll were both at atemperature of Tg−5° C. The atmosphere in the film formation was 25° C.and 60% RH.

Next, just before wound up, the film was trimmed on both sides thereof(by 5 cm of the overall width), and then knurled on both sides thereofto a width of 10 mm and a height of 20 μm. The final film width was 1540mm and the film was wound to a length of 450 m.

The COC films 1 to 3 and the comparative COC film C2 were analyzedaccording to the methods mentioned in the above to determine the tiltangle β[°] and also Re, Rth and the wavelength dispersioncharacteristics thereof. The results are shown in Table below.

TABLE 3 (11) (12) (13) COC film (MPa) (m/nin) (m/min) (14) 1 5 5.25 50.95 2 4 5.5 5 0.91 3 1 6 5 0.83 C2*1 — — 5 — (11) the touch pressure ofthe touch roll the material (12) the peripheral speed of the touch roll(13) the peripheral speed of the casting roll (14) the peripheral speedratio *1Any touch roll was not used.

TABLE 4 Wavelength Wavelength dispersion dispersion of β COC film Re(nm) Rth (nm) of Re *1 Rth *2 (°) 1 5 13 0.2 1.2 −15 2 3 16 0.1 1 −30 32 12 0.2 1.1 −45 C2 2 4 0.3 0.8 0 *1: |Re(630)-Re(450)| *2:|Rth(630)-Rth(450)|

3. Production Example for Polarizing Plate Production of PolarizingElement

A polyvinyl alcohol film having a thickness of 80 μm was dyed in anaqueous iodine solution having a concentration of 5% by mass (ratio bymass: iodine/potassium iodide=1/10). Next, this was dipped in an aqueoussolution containing 3% by mass of boric acid and 2% by mass of potassiumiodide, and stretched in an aqueous solution containing 4% by mass ofboric acid and 3% by mass of potassium iodide, by 6.0 times, andthereafter dipped in an aqueous solution of 5% by mass of potassiumiodide. Next, this was dried in an oven at 40° C. for 3 minutes to givea polarizing element having a thickness of 30 μm.

(Preparation of Aqueous Solution of Polyvinyl Alcohol Adhesive)

An aqueous solution containing 100 parts by mass of acetoacetylgroup-modified polyvinyl alcohol (having a degree of acetylation of 13%)and 20 parts by mass of methylolmelamine was prepared to have aconcentration of 0.5% by mass. This is an aqueous solution of polyvinylalcohol adhesive.

(Production of Polarizing Plate)

A cellulose resin (Eastman Chemical's, cellulose acetate propionate) wasdiluted in butyl acetate to prepare a solution having a solidconcentration of 7.5% by weight. The solution was applied onto onesurface of an acryl-base polymer film 1, and dried in an oven at 100° C.for 3 minutes to prepare a cellulose resin layer-coated, polarizingelement-protective film. The dry thickness of the cellulose resin layerwas 0.8 μm.

Using the aqueous solution of polyvinyl alcohol adhesive prepared in theabove, the above-mentioned acryl-base polymer film 1 was stuck to onesurface of the above-mentioned polarizing element, and a saponifiedtriacetyl cellulose (TAC) film (FUJIFILM's Fujitac T-60, having athickness of 60 μm) was to the other surface thereof. This was dried at70° C. for 10 minutes to produce a polarizing plate, Polarizing Plate 1.

Polarizing Plates 2, 3 and C1 were produced in the same manner as thatfor Polarizing Plate 1, for which, however, the acryl-base polymer film1 was changed to the acryl-base polymer film 2, 3 or C1. PolarizingPlates 4 to 6 were produced also in the same manner as above, in which,however, the sticking angle of the acryl-base polymer films 1 to 3 wereshifted by 180 degrees so that β could be negative.

A polarizing plate, Polarizing Plate 7, was produced also in the samemanner as above, in which, however, the acryl-base polymer film 1 waschanged to the acryl-base polymer film 4.

Using the aqueous solution of polyvinyl alcohol adhesive prepared in theabove, a saponified triacetyl cellulose (TAC) film (FUJIFILM's FujitacT-60, having a thickness of 60 μm) was stuck to both surfaces of thepolarizing element prepared in the above, thereby producing a polarizingplate, Polarizing Plate R1.

Using the aqueous solution of polyvinyl alcohol adhesive prepared in theabove, a saponified triacetyl cellulose (TAC) film (FUJIFILM's FujitacT-60, having a thickness of 60 μm) was stuck to one surface of thepolarizing element prepared in the above, and using an adhesive, abiaxial film prepared by stretching TAC was stuck to the other surfacethereof, thereby producing a polarizing plate, Polarizing Plate R2.

Using the aqueous solution of polyvinyl alcohol adhesive prepared in theabove, the COC film 1 was stuck to one surface of a polarizing element,and a saponified triacetyl cellulose (TAC) film (FUJIFILM's FujitacT-60, having a thickness of 60 μm) was to the other surface thereof.This was dried at 70° C. for 10 minutes to produce a polarizing plate,Polarizing Plate 8. Polarizing Plates 9, 10 and C2 were produced in thesame manner as that for Polarizing Plate 8, for which, however, the COCfilm 1 was changed to the COC film 2, 3 or C2.

4. Production of Liquid-Crystal Display Device PRODUCTION EMBODIMENT 1Examples 1 to 3, and Comparative Example 1

An IPS-mode liquid-crystal display device having the same constitutionas in FIG. 1 was produced. Concretely, as the polarizing plates PL1 andPL2 in FIG. 1, any of Polarizing Plates 1 to 3 produced in the above wasused. More concretely, this is as follows:

An electrode pattern was formed on one glass substrate in such a mannerthat the distance between the adjacent electrode lines could be 20 μm, apolyimide film was provided thereon as an alignment film, and this wasrubbed. A polyimide film was provided on one surface of another glasssubstrate and rubbed to be an alignment film. The two glass substrateswere combined to be a cell in such a manner that their alignment filmscould face each other and that the rubbing direction thereof could be inparallel to each other. Then, a nematic liquid crystal compositionhaving a refractivity anisotropy (Δn) of 0.0888 and a positivedielectric anisotropy (Δ∈) of 4.5 was sealed in the cell so that thecell gap d could be 3.5 μm, thereby producing a liquid-crystal cellhaving Δn×d of 311 nm. The pretilt was 1°.

Two sheets of Polarizing Plate 1 produced in the above were prepared,and disposed on and below the liquid-crystal layer to sandwich ittherebetween. In this, the upper and lower polarizers were so disposedthat their absorption axes could be perpendicular to each other. Theacryl-base polymer film 1 faced the liquid-crystal cell side. In this,the members were so disposed that the pretilt direction of theliquid-crystal cell could be the same as the β direction of theacryl-base polymer film. The process gave an IPS-mode liquid-crystaldisplay device 1 of Example 1.

Liquid-crystal display devices 2 and 3 having the same constitution asin FIG. 1 were produced in the same manner as that for theliquid-crystal display device 1, for which, however, Polarizing Plate 1was changed to Polarizing Plate 2 or 3.

A liquid-crystal display device C1 of Comparative Example having thesame constitution as in FIG. 1 was produced in the same manner as thatfor the liquid-crystal display device 1, for which, however, PolarizingPlate 1 was changed to Polarizing Plate C1.

PRODUCTION EMBODIMENT 2 Examples 4 to 6, and Comparative Example 2

An IPS-mode liquid-crystal display device having the same constitutionas in FIG. 2 was produced. Concretely, as the polarizing plate PL1′ inFIG. 2, Polarizing Plate R1 produced in the above was used. As the film16 in FIG. 2, JSR's Arton film (Re=200 nm, Rth=−30 nm) was used. Aspolarizing plate PL2 in FIG. 2, any of Polarizing Plates 4 to 6 producedin the above was used. The others were the same as in ProductionEmbodiment 1, and liquid-crystal display devices 4 to 6 were producedherein. In this, the members were so disposed that the pretilt directionof the liquid-crystal cell could be opposite to the β direction of theacryl-base polymer film (in the mirror-symmetric direction to eachother).

A liquid-crystal display device C2 of Comparative Example was producedin the same manner as that for the liquid-crystal display device 4, forwhich, however, Polarizing Plate 4 was changed to Polarizing Plate C1.

PRODUCTION EMBODIMENT 3 Example 7, and Comparative Example 3

An IPS-mode liquid-crystal display device having the same constitutionas in FIG. 3 was produced. Concretely, as the polarizing plate PL1″ inFIG. 3, Polarizing Plate R2 produced in the above was used. As theprotective film 14′ in FIG. 3, a biaxial film prepared by stretchingTAC(Re=61 nm, Rth=194 nm) was used; and as the positive C-plate 18, afilm having Re=0 nm and Rth=240 nm was used. As polarizing plates PL2 inFIG. 3, Polarizing Plate 7 produced in the above was used. The otherswere the same as in Production Embodiment 1, and a liquid-crystaldisplay device 7 was produced herein. In this, the members were sodisposed that the pretilt direction of the liquid-crystal cell could bethe same as that of the β direction of the acryl-base polymer film.

A liquid-crystal display device C3 was produced in the same manner asthat for the liquid-crystal display device 7, for which, however,Polarizing Plate 7 was changed to Polarizing Plate C1.

PRODUCTION EMBODIMENT 4 Examples 8 to 10

An IPS-mode liquid-crystal display device having the same constitutionas in FIG. 1 was produced. Concretely, as the polarizing plates PL1 andPL2 in FIG. 1, any of Polarizing Plates 8 to 10 produced in the abovewas used. The others were the same as in Production Embodiment 1, andliquid-crystal display devices 8 to 10 were produced herein. In this,the members were so disposed that the pretilt direction of theliquid-crystal cell could be opposite to the β direction of the COC film(in the mirror-symmetric direction to each other).

A liquid-crystal display device C4 was produced in the same manner asthat for the liquid-crystal display device 8, for which, however,Polarizing Plate 8 was changed to Polarizing Plate C2.

5. Evaluation of Liquid-Crystal Display Device

The liquid-crystal display devices produced in the above were tested forlight leakage at the time of black level of display thereof, in themanner mentioned below.

As in FIG. 4( a), the azimuth angle direction was taken at 45°, 135°,225° and 315° on the panel surface; and as in FIG. 4( b), the level oflight leakage at the time of black level of display in the direction asrotated to the polar angle of 60° from the normal direction wasdetermined, using a color brightness meter (Topcon's BM-5). The resultsare shown in the Table below.

TABLE 5 β Light leakage (%)*1 Example LCD Structure Polarizing plate (°)45° 135° 225° 315° 1 1 FIG. 1 1 15 1.08 1.08 1.26 1.26 2 2 FIG. 1 2 301.12 1.12 1.23 1.23 3 3 FIG. 1 3 45 1.14 1.14 1.21 1.21 Comparison 1 C1FIG. 1 C1 0 1.02 1.02 1.31 1.31 4 4 FIG. 2 4 −15 0.27 0.27 0.33 0.33 5 5FIG. 2 5 −30 0.31 0.31 0.32 0.32 6 6 FIG. 2 6 −45 0.34 0.34 0.33 0.33Comparison 2 C2 FIG. 2 C1 0 0.24 0.24 0.36 0.36 7 7 FIG. 3 7 10 0.180.18 0.16 0.16 Comparison 3 C3 FIG. 3 C1 0 0.16 0.16 0.19 0.19 8 8 FIG.1 8 −15 0.95 0.95 1.09 1.09 9 9 FIG. 1 9 −30 1.02 1.02 1.04 1.04 10  10 FIG. 1 10  −45 1.10 1.10 1.01 1.01 Comparison 4 C4 FIG. 1 C2 0 0.87 0.871.15 1.15 *1the amount of light leakage in the direction with a polarangle of 60 degrees and an azimuth angle of 45, 135, 225 or 315 degrees.

The above results confirm that the liquid-crystal display devices 1 to 3and 8 to 10 of Examples of the invention were improved over theliquid-crystal display devices C1 and C4 of Comparative examples, inpoint of the symmetricity in light leakage in four azimuth angledirections. These also confirm that the liquid-crystal display devices 4to 7 of Examples of the invention had little light leakage and were alsoimproved over the liquid-crystal display devices C2 and C3 ofComparative Examples in point of the symmetricity thereof.

FFS-mode liquid-crystal display devices were produced and evaluated inthe same manner as above, and it was confirmed that they had littlelight leakage were improved in point of the symmetricity.

Liquid-crystal display devices 11 to 20 and C5 to C8 were produced underthe same conditions for the laminate structure, the polarizer and β asin Examples 1 to 10 and Comparative Examples 1 to 4, for which, however,the pretilt of the liquid-crystal cell was changed to 5°. These areExamples 11 to 20 and Comparative Examples 5 to 8.

TABLE 6 β Light leakage (%)*1 Example LCD Structure Polarizing plate (°)45° 135° 225° 315° 11 11 FIG. 1 1 15 0.73 0.73 2.12 2.12 12 12 FIG. 1 230 0.77 0.77 2.10 2.10 13 13 FIG. 1 3 45 0.79 0.79 2.09 2.09 Comparison5 C5 FIG. 1 C1 0 0.67 0.67 2.15 2.15 14 14 FIG. 2 4 −15 0.15 015 0.720.72 15 15 FIG. 2 5 −30 0.19 0.19 0.7 0.7 16 16 FIG. 2 6 −45 0.22 0.220.71 0.71 Comparison 6 C6 FIG. 2 C1 0 0.11 0.11 0.75 0.75 17 17 FIG. 3 710 0.3 0.3 0.44 0.44 Comparison 7 C7 FIG. 3 C1 0 0.28 0.28 0.46 0.46 1818 FIG. 1 8 −15 0.63 0.63 2.01 2.01 19 19 FIG. 1 9 −30 0.68 0.68 2.012.01 20 20 FIG. 1 10  −45 0.69 0.69 2.02 2.02 Comparison 8 C8 FIG. 1 C20 0.56 0.56 2.05 2.05 *1the amount of light leakage in the directionwith a polar angle of 60 degrees and an azimuth angle of 45, 135, 225 or315 degrees.

The data confirm that the liquid-crystal display devices of Examples ofthe invention were also improved over the comparative liquid-crystaldisplay devices in point the symmetricity thereof when the pretilt ofthe liquid-crystal cell was 5°. The same applies also to theliquid-crystal display devices where the pretilt of the liquid-crystalcell was 0.5°.

The invention claimed is:
 1. An optical compensation film for IPS orFFS-mode liquid crystal display devices, having a tilt angle β[°]satisfying 0<|β|45═, β[°] being defined as φ giving the minimum value ofretardation R[φ] which is retardation measured for incident light comingin a direction tilted by φ° from a normal line relative to thefilm-plane, with the in-plane slow axis of the optical compensation filmas a rotation axis; having retardation in plane at a wavelength of 550nm, Re(550), of from −10 nm to 10 nm; and having retardation along thethickness direction at a wavelength of 550 nm, Rth(550), of from −30 nmto 30 nm, provided that Rth(550) is not equal to zero.
 2. The opticalcompensation film for IPS or FFS-mode liquid crystal display devices ofclaim 1, of which the wavelength dispersion characteristics of Re,|Re(630)−Re(450)|, is equal to or less than 1.5 nm, and the wavelengthdispersion characteristics of Rth, |Rth(630)−Rth(450)|, is equal to orless than 4 nm.
 3. The optical compensation film for IPS or FFS-modeliquid crystal display devices of claim 1, which is an acryl-basepolymer film.
 4. The optical compensation film for IPS or FFS-modeliquid crystal display devices of claim 3, comprising as a majoringredient, an acryl-base polymer having at least one unit selected fromthe group consisting of lactone ring unit, maleic anhydride unit, andglutaric anhydride unit.
 5. The optical compensation film for IPS orFFS-mode liquid crystal display devices of claim 1, which comprises acycloolefin polymer-base film.
 6. An IPS or FFS-mode liquid crystaldisplay device comprising: a pair of substrates at least one of whichhas an electrode and which are disposed to face each other, theelectrode forming an electric field having a component parallel to theelectrode-having substrate; an alignment-controlled liquid-crystal layerdisposed between the pair of substrates; and a pair of polarizersdisposed to sandwich the liquid-crystal layer therebetween; wherein atleast one of the pair of polarizers has at least one opticalcompensation film of claim
 1. 7. The IPS or FFS-mode liquid crystaldisplay device of claim 6, wherein Δn×d is from 250 nm to 400 nm,wherein Δn represents the birefringence of liquid-crystal molecules inthe liquid-crystal layer and d represents the thickness of theliquid-crystal layer.
 8. The IPS or FFS-mode liquid crystal displaydevice of claim 6, wherein the pretilt angle of liquid-crystal moleculesin the liquid-crystal layer is from 0.2 to 10°.
 9. An IPS or FFS-modeliquid-crystal display device comprising: a pair of polarizing elements,a liquid-crystal cell as horizontally aligned between the pair ofpolarizing elements, and an optical compensation film of claim 1individually between each of the pair of polarizing elements and theliquid-crystal cell.
 10. An IPS or FFS-mode liquid-crystal displaydevice comprising: a pair of polarizing elements, a liquid-crystal cellas horizontally aligned, disposed between the pair of polarizingelements, a film of claim 1 disposed between one of the pair ofpolarizing elements and the liquid-crystal cell, and anoptically-biaxial film and a positive C-plate between the other of thepair of polarizing elements and the liquid-crystal cell.
 11. The opticalcompensation film for IPS or FFS-mode liquid crystal display devices ofclaim 1, which has the thickness of from 20 μm to 200 μm.
 12. Theoptical compensation film for IPS or FFS-mode liquid crystal displaydevices of claim 1, which has the thickness unevenness of from 0% to 3%.13. The optical compensation film for IPS or FFS-mode liquid crystaldisplay devices of claim 1, which has a mean film width of from 1 m to 3m.
 14. The optical compensation film for IPS or FFS-mode liquid crystaldisplay devices of claim 1, which has the film width fluctuation of from1% to 15%.
 15. The optical compensation film for IPS or FFS-mode liquidcrystal display devices of claim 1, which has height of knurl of from 1μm to 50 μm.
 16. The optical compensation film for IPS or FFS-modeliquid crystal display devices of claim 1, which has width of knurl offrom 1 mm to 50 mm.
 17. The optical compensation film for IPS orFFS-mode liquid crystal display devices of claim 1, having retardationin plane at a wavelength of 550 nm, Re(550), of from 0 nm to 5 nm. 18.The optical compensation film for IPS or FFS-mode liquid crystal displaydevices of claim 1, wherein 0<|β|≦35°.
 19. The optical compensation filmfor IPS or FFS-mode liquid crystal display devices of claim 1, wherein0<|β|≦30°.
 20. A polarizing plate for IPS or FFS-mode liquid crystaldisplay devices comprising at least a polarizing element and the opticalcompensation film of claim 1.